hypothesis on drinking water

• Open access
• Published: 29 January 2020

Trends in tap and bottled water consumption among children and adults in the United States: analyses of NHANES 2011–16 data

• Florent Vieux 1 ,
• Matthieu Maillot 1 ,
• Colin D. Rehm 2 ,
• Pamela Barrios 3 &
• Adam Drewnowski 4  

Nutrition Journal volume  19 , Article number:  10 ( 2020 ) Cite this article

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Dietary Guidelines for Americans 2015–20 recommend choosing water in place of sugar-sweetened beverages (SSB). This study examined water consumption patterns and trends among children and adults in the US.

Dietary intake data for 7453 children (4-18y) and 15,263 adults (>19y) came from two 24 h dietary recalls in three cycles of the National Health and Nutrition Examination Survey (NHANES 2011–2016). Water was categorized as tap or bottled (plain). Other beverages were assigned to 15 categories. Water and other beverage intakes (in mL/d) were analyzed by sociodemographic variables and sourcing location. Consumption time trends from 2011 to 2016 were also examined. Total water intakes from water, other beverages and moisture from foods (mL/d) were compared to Dietary Reference Intakes (DRI) for water.

Total dietary water (2718 mL/d) came from water (1066 mL/d), other beverages (1036 mL/d) and from food moisture (618 mL/d). Whereas total water intakes remained stable, a significant decline in SSB from 2011 to 2016 was fully offset by an increase in the consumption of plain water. The main sources of water were tap at home (288 mL/d), tap away from home (301 mL/d), and bottled water from stores (339 mL/d). Water and other beverage consumption patterns varied with age, incomes and race/ethnicity. Higher tap water consumption was associated with higher incomes, but bottled water was not. Non-Hispanic whites consumed most tap water (781 mL/d) whereas Mexican Americans consumed most bottled water (605 mL/d). Only about 40% of the NHANES sample on average followed US recommendations for adequate water intakes.

The present results suggest that while total water intakes among children and adults have stayed constant, drinking water, tap and bottled, has been replacing SSB in the US diet.

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Introduction

The Dietary Guidelines for Americans 2015–2020 have encouraged consumers to choose beverages with no added sugars, such as water, in place of sugar-sweetened beverages (SSB) [ 1 ]. Dietary intake surveys in the US have pointed to a continuing decline in SSB consumption [ 2 , 3 ], especially among children, teenagers, and young adults [ 3 , 4 , 5 , 6 ]. However, SSB consumption rates are still relatively high among racial/ethnic minorities and younger age groups and continue to be associated with higher obesity risk [ 3 , 4 , 6 ].

Replacing SSB with plain drinking water has become central to health promotion strategies, including those led by US federal agencies [ 1 ]. The Healthy, Hunger-Free Kids Act of 2010 [ 7 ] requires schools participating in the National School Lunch Program [ 8 ] to make free water available to students during meal times. The federal standards also require schools in the School Breakfast Program to make drinking water available when breakfast is served in the cafeteria [ 9 ]. Schools are encouraged to ensure that water fountains are clean and properly maintained, provide access to water fountains, dispensers, and hydration stations throughout the school, and allow students to have water bottles in class or to go to the water fountain [ 10 ]. Drinking fountains in public spaces are also viewed as an opportunity for public health. Much of the federal emphasis has been on plain drinking water from the tap.

Compared to the extensive literature on SSB consumption [ 2 ], less is known about consumption patterns and trends for drinking water, tap and bottled, among US children and adults. Past studies [ 11 ] have estimated that 56% of plain drinking water in the US comes from the tap, whereas 44% is bottled. Industry sources suggest that sales of bottled water have increased since then and that the global market for bottled water has grown substantially [ 12 ]. Analyses of the most recent National Health and Nutrition Examination Survey (NHANES) data would provide insights into the current tap and bottled water consumption trends in the US [ 11 , 13 ].

The present hypothesis was that the reported decline in SSB consumption may have been offset, in part or in full, by a compensatory increase in drinking water. Such a finding would provide insight into the effectiveness of public health policies in the US [ 1 ]. The position of the Centers for Disease Control is that adequate water intakes would help increase overall water consumption, maintain hydration status, and reduce added sugar content of the diet, if substituted for SSB [ 10 ]. When it comes to maintaining hydration, examining compliance with standards and norms expressed either as water intakes in mL/d or as ratio on water intakes to calories (kcal/d) would be of additional interest. The question was whether any population subgroup was failing to maintain adequate water intakes, as specified by the Institute of Medicine (IOM).

The present analyses were based on the nationally representative NHANES 2011–2016 dietary intakes database for children (4-18y) and adults (≥19y) in the US, including the most recent 2015–2016 cycle [ 14 ]. The present goals were to examine consumption patterns for water and other beverages by socio-demographic variables, including education and incomes and to explore consumption trends between 2011 and 2016. The adequacy of total water intakes, as compared to the IOM recommendations was also examined.

Dietary intake databases

Consumption data for drinking water, beverages, and foods came from three cycles of the nationally representative NHANES, corresponding to years 2011–12, 2013–2014, and 2015–2016 [ 15 ]. The three NHANES cycles provided a nationally representative sample of 7453 children (aged 4-18y) and 15,263 adults (aged >19y).

The NHANES 24-h recall uses a multi-pass method, where respondents reported the types and amounts of all food and beverages consumed in the preceding 24-h from midnight to midnight [ 16 ]. The multi-pass method was conducted by a trained interviewer using a computerized interface [ 17 ]. Respondents first identified a quick list of foods and beverages consumed. The time and occasion for each food item was also obtained. A more detailed cycle then recorded the amounts consumed, followed by a final probe for any often-forgotten foods (beverages, condiments). Day one interviews were conducted by trained dietary interviewers in a mobile examination center. Day two interviews were conducted by telephone some days later [ 18 ].

For children 4-5y, dietary recall was completed entirely by a proxy respondent (i.e. parent or guardian with knowledge of the child’s diet) [ 16 ]. Proxy assisted interviews were conducted with children 6–11 years of age. Children 12-19y were the primary source of dietary recall but could be assisted by an adult who had knowledge of their diet.

We used a combination of the one-day value and the two-day mean to make use of all available dietary data. About 90% of people had two recalls. This method included all NHANES participants, even those without a second recall. Water consumers were defined as those NHANES participants who were drinking water on day one, day two, or both.

Participant characteristics

NHANES participants were stratified by gender and age. The age group cut-points were: 4-8y, 9-13y, 14-18y, 19-30y, 31-50y, 51-70y, and > 70y. These age groups generally correspond to the age groups used by the IOM. Race/ethnicity was defined as: non-Hispanic white, non-Hispanic black, Mexican American, other Hispanic, and other/mixed race. Family income-to-poverty ratio (IPR) is the ratio of family income to the federal poverty threshold; the cut-points for IPR were < 1, 1–1.99, 2–3.49, and ≥ 3.5.

Water intakes from water and other beverages

Water and other beverages were classified into groups. Plain drinking water was split into tap and bottled. Other beverages were classified as follows: milk and milk beverages, milk substitutes (soy milk), citrus juices, non-citrus juices, diet soda, regular soda, ready-to-drink tea, ready-to-drink coffee, fruit drinks, sports drinks, energy drinks, hot tea/coffee, alcoholic beverage, enhanced water, and supplemental beverages. Common examples by beverage category are presented in Table  5 in Appendix. The present analyses were for water from water and other beverages only. For example, milk consumed with cereal (i.e. not as a beverage) was assigned to the foods category.

The NHANES 24-h recalls for each participant provided information on the amount in grams of each food and beverage consumed [ 14 ]. The present results were for mL of water content from water and selected beverages and not for the volume of the beverages themselves (which may not be 100% water). Moisture from foods was calculated as well.

The USDA Food and Nutrient Database for Dietary Studies (FNDDS) was used to calculate the energy content of the diet based on caloric beverages and solid foods [ 19 ]. These data were used to calculate the ratios of water intakes (mL/d) to energy intakes (kcal/d) for each NHANES participant.

Time trend analyses 2011–2016

Time trend analyses examined mean daily water intakes (mL/d) from tap and bottled water and water intakes from different beverage categories. Percent reported consumers for tap and bottled water was calculated as well, separately for each NHANES cycle.

Determination of adequate water intakes

In conventional analyses, the mean of two 24-h recalls does not represent the habitual intakes of an individual. Failing to meet water or nutrient recommendations on a particular day may not accurately reflect the long-term status of the individual. For that reason, the National Cancer Institute (NCI) method was used to characterize the usual intake of water from water, beverages and foods [ 20 , 21 , 22 ]. This method has been used in other studies to estimate the usual intake of nutrients and food groups, including the population distribution of intakes.

Sourcing location for water and other beverages

The following NHANES sourcing options for foods and other beverages were selected: store, work/school, someone else (e.g. friends’ home), quick-service restaurant (fast food), full-service restaurant, and other. Tap water does not have a source in NHANES; however, the source of water can be determined using information on the location of meals. For example, if a meal at a fast food restaurant was accompanied by tap water consumed at the same time, we can infer that the tap water was from “away from home”. Tap water consumed at home was coded as “at home”. For bottled water we created a variable called “home” or combined “store and home”, as most home-consumed foods are from the store. Tap water category “outside of home” was reserved for occasions when tap water was consumed away from home and with no other foods at the same time.

Data availability and ethical approval

The necessary IRB approval for NHANES had been obtained by the National Center for Health Statistics (NCHS) [ 23 ]. Adult participants provided written informed consent. Parental/ guardian written informed consent was obtained for children. Children/adolescents ≥12y provided additional written consent. All NHANES data are publicly available on the NCHS and USDA websites [ 14 ]. Per University of Washington (UW) policies, public data do not involve “human subjects” and their use requires neither IRB review nor an exempt determination. Such data may be used without any involvement of the Human Subjects Division or the UW Institutional Review Board.

Statistical analyses

The survey-weighted mean intakes of total water were evaluated overall and by age group, gender, race/ethnicity, and family income-to-poverty ratio. All analyses accounted for the complex survey design of NHANES and reflect dietary behaviors of the US adult population from 2011 to 16.

Analyses of what proportion of NHANES 2011–2016 participants met the IOM recommendations for adequate hydration were based on habitual water intakes established using the National Cancer Institute method [ 24 , 25 ]. The probability of water consumption was estimated to be 1. Subsequent analyses specified the consumption-day amount using linear regression and intake data from 24-h recalls.

The consumption of tap and bottled water was evaluated separately for the entire population and for population sub-groups. Survey-weighted means and corresponding standard errors were obtained. Hypothesis testing was based on a linear trend test which treats the NHANES cycles as a continuous variable. This trend test may be sensitive to extreme values in either the first (2011–12) or last (2015–2016) cycle and may not reflect weak non-linear trends. All analyses were conducted using SAS software, version 9.4 (SAS Institute Inc., Cary NC, USA) by using SURVEYREG, SURVEYMEANS and SURVEYFREQ procedures.

Total water intakes from water, other beverages, and foods

Table  1 shows total water intakes in mL/d by gender, age, socio-demographic groups, and eating occasion. Data are for total water intakes, water from water and other beverages, and moisture from foods. Total water intake was 2718 mL/d, of which 2100 mL/d (77%) came from water and other beverages and 618 mL/d (23%) came from food moisture. Men had higher water intakes from all sources than did women (2949 mL vs. 2495 mL; p  < 0.01). There was also a strong age effect. Total water intakes increased sharply with age, peaked for the 31–50y age group, and declined thereafter, dropping to 2355 mL/d after the age of 70y.

Non-Hispanic whites had highest total water intakes (2879 mL/d) and highest water intakes from water and other beverages (2266 mL/d). Non-Hispanic blacks had lowest total water intakes (2249 mL/d) and lowest water intakes from water and other beverages (1695 mL/d). Total water intakes followed a socioeconomic gradient. Groups with higher IPR had the highest total water intakes (2952 mL/d), had highest intakes of water and other beverages (2288 mL/d) and derived most moisture from foods (664 mL/d). The difference in total water intakes between IPR < 1 (2461 mL/d) and IPR > 3.49 was almost 500 mL/day. Adjusting for age, intakes were 2225 mL/d in the lowest IPR and 2548 mL/d in the highest IPR.

Table 2 shows intakes of water, now separated into tap and bottled water, by individual socio-demographic variables and eating occasion. Total intake of drinking water, both tap and bottled, was 1066 mL/d. Tap water supplied 661 mL/d whereas bottled water supplied 404 mL/d. Other beverages, caloric and non-caloric, supplied another 1034 mL/d. Thus, the daily distribution of dietary sources of water was tap water (24%), bottled water (14%), other beverages (38%), and food moisture (23%).

Men and women drank comparable amounts of tap and bottled water. There was a significant effect of age group. The consumption of tap and bottled water peaked at ages 31-50y and declined thereafter. People > 70 y old drank less water than other groups; there was an age-related decline in bottled water (212 mL/d) and other beverages (898 mL/d).

Although the consumption of drinking water increased with rising IPR, the income effect operated in opposite directions for tap water and for bottled water. Higher IPR was associated with more tap water (from 495 to 821 mL/d) but, unexpectedly, with somewhat lower consumption of bottled water (from 436 to 360 mL/d).

There were also differences in consumption of drinking water by race/ethnicity. Non-Hispanic whites consumed the most tap water and the least bottled water (781 mL/d and 328 mL/d, respectively). Mexican Americans and non-Hispanic blacks consumed more bottled water than tap water, as did other Hispanics.

Men consumed more other beverages than did women (1214 mL/d vs. 861 mL/d). Beverage consumption peaked at 51-70y and declined for >70y age group. Non-Hispanic whites drank the highest amounts of other beverages (1157 mL/d); non-Hispanic blacks drank the least (803 mL/d). Water consumption from other beverages increased with IPR.

Separate analyses of caloric SSB, estimated water consumption from SSB at 288 mL/d, with peak consumption observed among younger adults aged 19-30y (410 mL/d). Non-Hispanic blacks consumed the most water from SSB (368 mL/d); the other/mixed race group consumed the least (205 mL/d). Water from SSB was lower among higher income groups (209 mL/d) as compared to 390 mL/d among lowest income groups.

Time trends in SSB and water consumption 2011–2016

Table 3 shows time trends for water intake from water and other beverages for each NHANES cycle (2011–2016) and separately for children (4-18y) and for adults (>19y). Total water intakes did not change during this time period, remaining at approximately 2100 mL/d. However, there was a significant decline in the consumption of other beverages (from 1097 mL/d to 970 mL/d) that was especially pronounced for children (from 675 mL/d to 522 mL/d) and was significant for both children and for adults. That reduction in intake was largely caused by reduced consumption of SSB, which was highly significant among both children and adults. Children also consumed less water from non-SSB beverages. Analyses for trends were significant.

While total water intakes remained stable, the significant decline in SSB consumption was offset by a corresponding significant increase in the consumption of tap and bottled water. Among adults aged >19y, the increase in tap and bottled water consumption from 1126 mL/d to 1271 mL/d was statistically significant. A smaller increase (from 577 mL/d to 663 mL/d) among children aged 4-18y was not. The observed small increases in bottled water did not reach statistical significance.

Figure  1 shows time trends for water intakes from water and other beverages for each of the three NHANES cycles. Water has been separated into tap and bottled, whereas beverages are shown by category. The SSB category includes regular sodas, fruit drinks and ready to drink tea and coffee, and most sports and energy drinks. The data show that a progressive decline in beverages, including SSB has been compensated for by drinking water. Figure 1 a (top) shows absolute amounts in mL/d, whereas Fig.  1 b (bottom) shows the percent contribution of each water source to water intakes.

ab . ( a ) Absolute intakes in mL/d of water (tap and bottled) and other beverages and ( b ) percent contribution from water (tap and bottled) and other beverages by NHANES year (2011–2016) and beverage category. Data are for children and adults aged >4y

Water intakes from water and other beverages by age

Figure  2 summarizes water intakes from tap and bottled water and from different other beverage categories by age. The categories are listed in the figure key. Figure 2 a (top) shows water intakes in mL/d, whereas Fig.  2 b (bottom) shows the percent contribution of different beverages to water intakes for each age group.

ab . ( a ) Absolute intakes in mL/d of water (tap and bottled) and other beverages and ( b ) percent contribution from water (tap and bottled) and other beverages by age group and beverage category

Water, tap and bottled, provided about 50% of water intakes, excluding moisture from food. Caloric and non-caloric beverages provided between 508 mL/d and 1239 mL/d of water depending on age. The type of beverages consumed varied as a function of age. Figure 2 a shows that the consumption of milk was highest for the 4-8y age group and declined progressively with age. The consumption of 100% non-citrus juices (driven in large part by apple juice) and fruit drinks also declined with age. By contrast, the consumption of regular soda increased with age, peaked in early adult life (19-30y) and declined thereafter. The consumption of diet soda increased sharply after the age of 30y. The consumption of 100% citrus juice did not show much variation with age.

The consumption of presweetened ready-to-drink (RTD) tea increased with age. The consumption of RTD coffee was low. Sports drinks and energy drinks were consumed primarily by adolescents and by young adults. The consumption of brewed coffee and tea increased sharply after the age of 18y and so did the consumption of alcohol. Older adults (>70y) were getting as much as 412 mL/d of daily water (or 24% of water from beverages) from coffee and tea.

Figure 2 b shows clearly the age-related trends in water and beverage consumption. First, the consumption of milk, 100% fruit juice, and juice drinks declined with age, whereas the consumption of SSB and water increased. The 19–30y age group derived most water from tap and bottled water but also from SSB. However, both tap and bottled water consumption declined with age, replaced by tea and coffee and, to a lesser extent, by alcohol.

These age-related trends were compounded by socioeconomic status. Figure  3 shows that the amounts and types of beverages consumed varied with IPR. Figure 3 a (top) shows water intakes in mL/d, whereas Fig.  3 b (bottom) shows the percent contribution of different beverages to water intakes for each IPR group. There was a small IPR linked decline in the consumption of milk and citrus and non-citrus juices. There was a sharp drop in the consumption of SSB that was partly offset by higher consumption of diet soda. The proportion of water from fruit drinks, sports drinks, and energy drinks declined. By contrast higher IPR was associated with higher percent contributions from brewed coffee and tea, enhanced water, and alcohol.

ab . ( a ) Absolute intakes in mL/d of water (tap and bottled) and other beverages and ( b ) percent contribution from water (tap and bottled) and other beverages by IPR and beverage category

Source locations of water and other beverages

Most bottled water and other beverages (1076 mL/d or 75% of total) came from the store. Of this, 339 mL/d came from store-bought bottled water and 737 mL/d came from store bought other beverages. Figure  4 shows the distribution of store bought other beverages by category. Smaller amounts of other beverages and virtually no bottled water were obtained from restaurants (full-service [FSR] and quick-service [QSR]), work/school or someone else.

Percentage of participants meeting IOM adequate intake recommendations for water by age group

Tap water consumption (589 mL/d) was almost evenly split between tap water at home (288 mL/d) and tap water away from home (301 mL/d); as previously noted, it was not possible to differentiate tap water more finely due to the manner of data collection.

Meeting recommendations for adequate water intakes

These data analyses used the NCI method to establish habitual water intakes based on two 24 h recalls, following published procedures [ 25 ]. Based on the NCI method, only about 40% of the NHANES 2011–2016 sample met the IOM recommendations for adequate water intakes. Figure  5 shows the percent of participants within each age group that met IOM recommendations for adequate water intakes using the NCI method. Data for years 2011–2016 were pooled as there was little year-to-year variation. The data show that men aged >70y were least likely to meet the IOM recommendations; only 5.15% did so.

Distribution of other beverages by sourcing location and beverage category. NHANES 2011–2016

Table  4 shows that the observed water volume per 1000 kcal for most groups was between 1.4–1.6 L/1000 kcal, consistent with the desirable values (≥1.0 L/1000 kcal) as recommended by the IOM and by the European Food Safety Authority [ 24 , 25 , 26 ]. The only two age groups with values < 1.0 L/1000 kcal were children aged 4–13y. Higher water volume per 100 kcal was observed for non-Hispanic Whites and for groups with higher IPR. Non-Hispanic Black participants and lower IPR groups had lowest water volumes per 1000 kcal.

The present analyses, based on the most recent 2015–2016 NHANES data confirm that the consumption of SSB in the US continues to drop [ 1 , 6 , 27 , 28 ]. While SSB may not be the biggest source of dietary energy for anyone except teenagers, they are the main source of added sugars in the American diet [ 29 ]. The Dietary Guidelines for Americans 2015–20, along with a number of industry-led initiatives specifically called for making water the beverage of choice [ 1 , 30 ]. Replacing caloric SSB with plain drinking water has become a priority area for interventions in school and public health nutrition [ 6 ]. Sales of bottled water in the US are also reported to be on the rise [ 31 ].

The present analyses provide several new insights into water and other beverage consumption patterns and trends. First, total dietary water intakes from drinking water, other beverages, and foods have remained stable from 2011 to 2016. Total amounts of water and other beverages have also remained constant. We now show for the first time that the observed significant drop in SSB consumption has been offset by an increased consumption of plain drinking water. On the average, about 62% of drinking water came from the tap, a major increase from 56% observed in the 2005–2010 NHANES database [ 11 ].

Second, and contrary to expectations, tap water consumption was higher at higher incomes, whereas the consumption of bottled water was higher at lower incomes. Consistent with previous findings, non-Hispanic whites and higher income groups in the present study consumed the largest amounts of tap water [ 11 ]. By contrast, Mexican Americans drank the most bottled water and the least tap water. In previous analyses of NHANES data, water consumption, both bottled and tap, among adults was significantly associated with higher education and incomes. The present data showed that the income effect (IPR) now operated in opposite directions.

The continuing positive social gradient in tap water consumption is a cause for concern. Whereas bottled water is purified or filtered, packaged, sealed, and distributed through retail channels, municipal tap water is delivered through pipes from reservoirs, rivers or aquifers. The quality of tap water has been variable and found to be problematic, especially in lower-income areas [ 32 , 33 ]. There seems to be a growing perception, confirmed by research studies, that tap water is safe to drink only in affluent neighborhoods [ 32 , 34 ]. The CDC does not advise tap water for anyone with a compromised immune system [ 35 ]. Additional studies have pointed to concerns with copper and lead [ 36 ]. Making water the beverage of choice needs to be sensitive to the quality of the local water supply and to community resources, wants, and needs.

The inverse social gradient in bottled water consumption seems to be unique to the US. Studies with children in the UK showed that bottled water consumption was associated with higher household socioeconomic status (SES) [ 37 , 38 ]. A social gradient for bottled water was not observed in France [ 39 ]. A previous study based on French INCA data examined water and other beverage consumption patterns by breakfast, AM snack, lunch, PM snack, dinner, and evening snack [ 39 ]. Another study based on data from the UK used time intervals to determine temporal distribution of water and beverage intakes [ 37 ]. There is a need for more international comparisons on who drinks tap water as opposed to bottled water [ 40 ], with what meal, and at what time of day [ 11 , 37 , 39 ].

The present analyses further showed that the consumption of bottled water was strongly age dependent [ 11 , 13 ]. Highly consumed by teenagers and young adults, bottled water was replaced in later life by tea and coffee and to a lesser extent alcohol. Older adults > 70 y drank relatively little bottled water.

Finally, bottled water came mostly from the store. Very little bottled water came from fast food or full-service restaurants, or from work or school. This may change as schools may begin to use bottled water due to safety concerns [ 34 , 36 , 40 ]. By contrast, tap water was evenly split between tap at home and tap away from home.

The present analyses based on the NCI method showed that the IOM recommendations for adequate water intakes (AI) were met by only 40% of the US population on average, with numbers varying from 5 to 50% depending on age. The IOM AI values are set at 1700 mL/d for boys and girls in the 4-8y age group and 2.1 L/d for girls and 2.4 L/d for boys in the 9-13y age group [ 24 ]. For 14–18 year-olds, the AI values are 3.3 L/d for boys and 2.3 L/d for girls. The IOM reference values for water intake among adults are 2.7 L/d for women and 3.7 L/d for men [ 24 ]. The IOM AI goals are derived from the median intake of the US population whereas the European Food Safety Authority (EFSA) recommends a daily total water intake (water from food and beverages) of 2.5 L for men and 2.0 L for women to maintain urinary osmolality of 500 mOsmol/L.

In past analyses of NHANES 2005–2010 [ 11 ], younger adults exceeded or came close to satisfying the DRIs for water. The shortfall between IOM recommendations and reality has been reported as most acute for young children and for older adults [ 11 , 13 ]. Older men and women failed to meet the Institute of Medicine (IOM) AI values, with a shortfall in daily water intakes of 1218 mL and 603 mL respectively. Eighty-three percent of women and 95% of men ≥71y failed to meet the IOM AI values for water [ 11 ].

However, it must be noted that non-compliance with IOM guidelines does not indicate dehydration. The second criterion of adequate hydration, water volume in mL per 1000 kcal, did not fall short of desirable values. Whereas the standard IOM recommendation is at least 1.0 L per 1000 kcal, the observed values of ~ 1,5 L/1000 kcal were well above this threshold [ 24 ]. In NHANES 2005–2010 also, average water volume per 1000 kcal was 1.2–1.4 L/1000 kcal for most population sub-groups, higher than the suggested minimum levels of 1.0 L/1.000 kcal [ 11 ].

On the other hand, beverage consumption in the US has shown a steady decline. The decline has been most acute for SSB but has also been observed with milk and 100% orange juice. While the replacement of SSB with plain water does have the benefit of removing added sugar, consistent with the Dietary Guidelines goals, the replacement of milk or 100% juice with water may not have the same nutritional benefits. Total water intake below IOM recommended levels may also be a cause for concern, especially among older adults.

The present analyses had limitations. First, the NHANES data are based on self-report and are subject to random and systematic reporting errors. In particular, a 24-h recall may systematically underestimate water and other beverage intake, especially outside of meals since it is very difficult for individuals to remember exactly how much tap water they had outside of meals. Fluid-specific records, used in smaller scale studies, may provide higher quality data. The use of proxy respondents for children ages 4-5y and proxy assisted interviews for children 6–11 make the collection of accurate data especially challenging. The 2 days of dietary recalls used different methods to collect the data, which may affect the estimates of water consumption. Underreporting of water intakes would lead to overestimating the percent of adults who fail to meet the recommended intakes. However, the NHANES has the advantage of being based on a large, nationally representative population sample. The NHANES dataset forms the basis for dietary surveillance in the US.

The SSB in the US diet are in the process of being replaced by plain water, both tap and bottled. This is an encouraging finding when it comes to public health goals. However, water consumption patterns showed wide variations by socioeconomic status, age group, and race/ethnicity. Social marketing strategies to promote water consumption, tap or bottled, will need to take these factors into account.

Availability of data and materials

Data used in the study is publicly available through the NHANES database (at https://wwwn.cdc.gov/nchs/nhanes/continuousnhanes/default.aspx ).

Abbreviations

USDA Food and Nutrient Database for Dietary Studies

Full-service restaurant

Institute of Medicine

Income-to-Poverty Ratio

National Cancer Institute

National Health and Nutrition Examination Survey

Quick-service restaurant

Ready-to-drink

Socioeconomic status

Sugar-Sweetened Beverages

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All authors (FV, MM, CDR, PB, and AD) conceptualized study design, formulated analytical questions and contributed to the manuscript preparation. Colin Rehm created the dataset, while Florent Vieux and Matthieu Maillot performed the principal analyses. Adam Drewnowski acted as lead writer of the manuscript. All authors (FV, MM, CDR, PB and AD) reviewed and approved the manuscript

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Florent Vieux and Matthieu Maillot are employees of MS- Nutrition. Pamela Barrios is employed by PepsiCo Inc. Adam Drewnowski has received contracts, consulting fees and honoraria from entities both public and private with an interest in beverage consumption, including SSB and bottled water manufacturers and distributors such as PepsiCo, Nestle, and Danone. Colin D. Rehm has no conflicts to report. The views expressed in this work are those of the authors and do not necessarily reflect the position or policy of Pepsico Inc.

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Vieux, F., Maillot, M., Rehm, C.D. et al. Trends in tap and bottled water consumption among children and adults in the United States: analyses of NHANES 2011–16 data. Nutr J 19 , 10 (2020). https://doi.org/10.1186/s12937-020-0523-6

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An increasing body of evidence suggests that excreting a generous volume of diluted urine is associated with short- and long-term beneficial health effects, especially for kidney and metabolic function. However, water intake and hydration remain under-investigated and optimal hydration is poorly and inconsistently defined. This review tests the hypothesis that optimal chronic water intake positively impacts various aspects of health and proposes an evidence-based definition of optimal hydration.

Search strategy included PubMed and Google Scholar using relevant keywords for each health outcome, complemented by manual search of article reference lists and the expertise of relevant practitioners for each area studied.

The available literature suggest the effects of increased water intake on health may be direct, due to increased urine flow or urine dilution, or indirect, mediated by a reduction in osmotically -stimulated vasopressin (AVP). Urine flow affects the formation of kidney stones and recurrence of urinary tract infection, while increased circulating AVP is implicated in metabolic disease, chronic kidney disease, and autosomal dominant polycystic kidney disease.

In order to ensure optimal hydration, it is proposed that optimal total water intake should approach 2.5 to 3.5 L day −1 to allow for the daily excretion of 2 to 3 L of dilute (< 500 mOsm kg −1 ) urine. Simple urinary markers of hydration such as urine color or void frequency may be used to monitor and adjust intake.

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Introduction

Water is the largest constituent of the human body, representing roughly 40 to 62% of body mass [ 1 ]. Water balance is constantly challenged by transepidermal, respiratory, fecal and urinary losses, with mean daily water turnover of 3.6 ± 1.2 L day −1 [ 2 ] or 2.8 to 3.3 and 3.4 to 3.8 L day −1 in women, and men, respectively [ 3 ]. Only a small amount of water is produced in the body (metabolic water, 0.25 to 0.35 L day −1 [ 2 , 4 ]) and the human body has a limited capacity to store water; so water losses must be replaced daily. Thus, water has been called the ‘most essential’ nutrient [ 5 , 6 ].

The maintenance of body water balance is so critical for survival that the volume of the body water pool is robustly defended within a narrow range, even with large variability in daily water intake. Evidence for this effective defense is found in population studies [ 4 ], observations of habitual low- vs. high-volume drinkers [ 7 , 8 ], and water intake interventions [ 8 , 9 , 10 ], all of which demonstrate that large differences or changes in daily water intake do not appreciably alter plasma osmolality, thereby substantiating the stability of total body water volume. This tight regulation is governed by sensitive osmotic sensing mechanisms which trigger two key response elements: (1) the release of arginine vasopressin (AVP), which acts via vasopressin V2 receptors (V2R) on the renal collecting ducts, initiating renal water saving when water intake is low; (2) the triggering of the sensation of thirst to stimulate drinking.

Despite its importance, water is also referred to as a forgotten [ 11 , 12 ], neglected, and under-researched [ 13 ] nutrient. This is reflected by discrepancies between regional water intake recommendations [ 4 , 14 ], and the fact that these reference values represent Adequate Intakes (AIs). The AIs are based upon observed or experimentally derived estimates of average water intake with insufficient scientific evidence to establish a consumption target associated with a health risk or benefit. In practice, from the perspective of the general public, water may not even be visible in dietary guidelines (e.g., www.choosemyplate.gov ). The implicit message is that there is little or no need to pay attention to water intake except in extreme situations; thirst is implicitly assumed to be an adequate guide.

This review advances the hypothesis that optimal water intake positively impacts various aspects of health. We propose an evidence-based definition of optimal hydration as a water intake sufficient to avoid excessive AVP secretion and to ensure a generous excretion of dilute urine, sufficient to avoid chronic or sustained renal water saving. For many, this would imply drinking somewhat beyond physiological thirst and likely more than the often-repeated target of ‘eight glasses of water per day’ called into question by Valtin [ 15 ] and others for lack of supporting evidence-based health outcomes. Here, we review the existing evidence for two specific mechanisms of action of how increased water intake may impact health: (1) the direct effect of increased urine flow on kidney and urinary tract health, and (2) the indirect effect of lowering AVP concentration on kidney and metabolic function. We conclude with a proposal for a range of water intake that provides optimal hydration.

Literature review and search strategy

Searches for relevant literature were divided by subtopic. Each subtopic was investigated by a group of two to three authors and involved at least one expert with current, relevant clinical practice or recent research activity. Search strategy included PubMed and Google Scholar using relevant keywords for each health outcome (e.g., for kidney stones: kidney, stones, lithiasis, fluid, water, urine, flow, volume). This was accompanied by manual search of article reference lists and the publication knowledge and expertise of relevant practitioners for each area studied (e.g., nephrology, physiology, metabolic health). For health outcomes included in Tables 1 and 2 , only human studies (observational or interventional) were included; animal or mechanistic work is cited where relevant to describe or support a plausible mechanism. No systematic assessment of study quality was performed. The initial search included articles available through the end of 2018; however, subsequent modifications to the manuscript resulted in the inclusion of some more recent references.

Direct effect of increased water intake to increase urine flow

While total body water and plasma osmolality are defended within a narrow range, urine volume adjusts water losses to compensate for fluctuations in daily water intake and insensible losses. Urine output adjusts quickly to changes in water intake, and 24-h urine volume is a reasonable surrogate marker for high or low daily water intake in healthy adults in free-living conditions [ 16 ]. Here, we review the evidence for the importance of high urine flow in the secondary prevention of kidney stones and urinary tract infection. A detailed description of individual studies is provided in Table 1 .

Kidney stones

Kidney stones are hard crystalline mineral deposits that form inside the kidney or urinary tract. They occur in 10% of the population worldwide [ 17 ] and recurrence is high: 40 to 60% of stone formers will relapse within 5 years following a first episode [ 18 , 19 , 20 ]. Stone formation results from dietary, genetic and/or environmental factors. In particular, low fluid intake and low urine volume have been shown to be significant risk factors for kidney stones in first-time and recurrent stone formers (Table 1 ) [ 21 , 22 , 23 , 24 ]. Mechanistically, low urine volume leads to higher concentrations of urinary solutes and promotes urine supersaturation, favoring crystal nucleation and stone growth [ 25 ]. Conversely, increased water intake facilitates the flushing of crystals by increasing urine flow.

In a 5-year randomized controlled trial (RCT), patients were either instructed to increase water intake to achieve a urine volume of 2 L day −1 without any further dietary changes or were assigned to a control group receiving no intervention [ 23 ]. Over the follow-up period, the recurrence of stones was lower (12%) in the intervention group, who maintained a urine volume of more than 2.5 L day −1 , compared with the control group (27% recurrence) whose urine volume remained at about 1.2 L day −1 . Two systematic reviews on this topic have concluded that high water intake reduces long-term risk of kidney stone recurrence [ 26 , 27 ]. In agreement with these findings, the European Association of Urology and the American Urological Association current guidelines for the secondary prevention of kidney stones recommend stone-formers maintain a fluid intake that will achieve a urine volume of at least 2.0 to 2.5 L daily [ 28 , 29 ]. Interestingly, increasing fluid intake also appears to be perceived as one of the easiest lifestyle changes to make with respect to stone recurrence. While dietary factors also influence stone formation, patients with recurrent kidney stones reported being more confident in their ability to increase fluid intake, compared to changing other dietary factors or taking medicine [ 30 ].

In terms of primary prevention, we are only aware of one study investigating the effects of increased habitual fluid intake [ 31 ]. In an area of Israel with a high incidence of urolithiasis, healthy inhabitants of one town participated in an education program that encouraged adequate fluid intake, while inhabitants of a second town did not participate in the program. At the end of the 3-year study period, urine output was found to be higher and incidence of urolithiasis lower in the intervention group compared with the control group. To date, no recommendation for primary stone prevention has been proposed. However, considering the aggregate of observational evidence, including a successful RCT for secondary prevention, as well as a clear mechanism of urine dilution to avoid supersaturation and stone formation, increased water intake among low drinkers in general would appear to be a reasonable, easy and cost-effective way to reduce urolithiasis recurrence in known stone formers [ 32 ] as well as in primary prevention [ 33 ].

Urinary tract infection

Urinary tract infections (UTI) are bacterial contaminations of the genitourinary tract affecting a large part of the female population and resulting in general discomfort and decreased quality of life. Increased water intake is sometimes recommended in clinical practice as a preventive strategy for UTI in women suffering recurrent events. However, the empirical evidence for any relationship between UTI and water intake or urinary markers of hydration is equivocal. Several non-randomized studies reported that low intake of fluids or reduced number of daily voids are associated with increased risk of UTI [ 34 , 35 , 36 , 37 , 38 ]. In contrast, other published data show no association between fluid intake and the risk of UTI, no difference in fluid intake between women with recurrent infections and healthy controls, and no effect of increased water intake on UTI risk [ 39 , 40 ]. A small crossover trial published in 1995 demonstrated that self-assessment of urine concentration encouraged lower urine osmolality and reduced frequency of UTI [ 41 ]; however, the study had a number of methodological problems including large number of participants lost to follow-up, lack of a proper control group, and not reporting fluid intake.

Recently, Hooton et al. published the first RCT assessing the effect of increased water intake on the frequency of acute uncomplicated lower UTI in premenopausal women [ 42 ]. One hundred and forty women suffering from recurrent UTI with low fluid intake and low urine volume were randomly assigned to increase their daily water intake by 1.5 L or to maintain their usual intake for 12 months. Increasing water intake (to 2.8 L day −1 ) and urine volume (to 2.2 L day −1 ) resulted in a 48% reduction in UTI events. Of note, a second benefit to increasing water intake was a reduction of antibiotic use, for prophylaxis or treatment of UTI. The proposed mechanism for the improvement in UTI recurrence was that increasing void frequency and urine volume facilitated the flushing of bacteria and thus reduced bacterial concentration in the urinary tract. More recently, a second study of elderly patients in residential care homes found that encouraging increased fluid intake by implementing structured ‘drink rounds’ multiple times per day reduced UTIs requiring antibiotics by 58%, and UTIs requiring hospital admission by 36% [ 43 ]. While the study did not measure individual increases in fluid intake during the intervention, the magnitude of reduction in UTI is substantial, and similar to that reported by Hooton et al. in a younger population, supporting the role for increased fluid intake in the secondary prevention of UTI.

Take home points

Increasing fluid intake is effective in the secondary prevention of kidney stones and urinary tract infection. Little is known about whether high fluid intake is also effective in primary prevention.

Mechanistically, increasing fluid intake results in lower urine concentration and increased urine flow. The former may be important in preventing supersaturation and crystal formation, while the latter encourages frequent flushing of the urinary tract which may be helpful for both kidney stone and UTI prevention.

European and American urological associations encourage maintaining a fluid intake sufficient to produce 2 to 2.5 L of urine per day to reduce risk of stone formation.

Indirect effect of increased water intake: mechanisms mediated by reducing circulating AVP

AVP is a critical hormone for the regulation of body fluid homeostasis. It can be secreted in response to small fluctuations of serum osmolality and primarily regulates fluid volume through its antidiuretic action on the kidney. Binding of AVP to the V2-receptors (V2R) located in the renal collecting ducts, induces translocation of aquaporin-2 to the cellular membrane and allowing increased water reabsorption [ 44 ] and the defense of total body water and plasma osmolality. Copeptin, a stable C-terminal fragment of the AVP precursor hormone released in a 1:1 ratio with AVP, is a surrogate marker for AVP secretion [ 45 ]. The recent availability of an ultra-sensitive assay for copeptin has dramatically increased research on AVP or copeptin and health outcomes. Lower circulating copeptin is associated with improved metabolic and renal outcomes (Table 2 ).

AVP and metabolic dysfunction

In addition to its well-defined role in concentrating urine and regulating body water via the V2R, AVP also acts on other AVP receptors (V1aR and V1bR) which occur in a variety of central and peripheral tissues, with multiple and wide-ranging physiological effects [ 46 ]. AVP may play an important role in the development of metabolic disease because it stimulates hepatic gluconeogenesis and glycogenolysis through V1aR [ 47 , 48 ] and triggers release of both glucagon and insulin through V1bR in pancreatic islets [ 49 ]. Moreover, AVP stimulates the release of adrenocorticotrophic hormone (ACTH) via V1bR in the anterior pituitary gland, thereby leading to elevated adrenal cortisol secretion and prompting undesirable cortisol-mediated gluconeogenesis [ 50 , 51 ].

High plasma copeptin levels have been associated with insulin resistance and metabolic syndrome in cross-sectional population and community-based studies [ 52 , 53 ]. Pooled data from three large European cohorts also show that participants in the top tertile of copeptin have higher fasting plasma glucose compared to the bottom and medium tertiles, and are more likely to have type 2 diabetes (T2DM) [ 54 ]. Moreover, copeptin has been consistently identified as an independent predictor of T2DM in four European cohorts (Table 2 ) [ 55 , 56 , 57 , 58 ], suggesting that AVP contributes to the development of the disease. Furthermore, within diabetic patients, individuals with the highest copeptin level had higher HbA1c levels [ 59 ], were more likely to develop metabolic complications, heart disease, death and all-cause mortality [ 60 , 61 ].

A causal role for AVP in metabolic disorders is supported by preclinical evidence showing that high AVP concentration impairs glucose regulation in rats, an effect reversed by treatment with a selective V1aR antagonist [ 62 , 63 ]. In humans, causality is also supported by recent evidence from a Mendelian randomization approach study which reported that certain single nucleotide polymorphisms within the AVP-neurophysin II gene were associated with both higher AVP and higher incidence of impaired fasting glucose in men, but not in women [ 56 ].

Individuals with lower habitual fluid intake have higher AVP levels compared to those who consume more fluids, despite similar plasma osmolality [ 7 , 64 ], and increasing plain water intake can lower AVP or copeptin over hours, days, or weeks [ 10 , 64 , 65 ]. Compellingly, the most substantial reductions in copeptin appear to occur in those with insufficient water intake as indicated by high baseline urine osmolality, low urine volume and/or higher baseline copeptin level [ 65 , 66 ]. Epidemiological evidence is inconsistent: low water intake is linked with increased risk of new-onset hyperglycemia [ 67 ], and an association between plain water intake and elevated glycated hemoglobin has been noted in men, but not women [ 68 ]. Pan et al. also found no association between plain water intake and incident T2DM in a large cohort of women [ 69 ]. In the short-term, a six-week pilot study in adults with high urine osmolality, low urine volume, and high copeptin, demonstrated that increasing water intake reduced circulating copeptin and resulted in a small but significant reduction in fasting plasma glucose, but no changes in fasting plasma insulin or glucagon [ 66 ]. However, a recent perspective paper pointed out that different manipulations to hydration have produced inconsistent results, suggesting that the relationship between water intake, hydration, AVP and metabolic response may be more complex [ 70 ].

Overall, there is convergent epidemiological evidence and a plausible mechanism for how higher circulating AVP may contribute to increased risk for metabolic disease. There is also evidence from short-term studies that in individuals with higher AVP, increasing water intake can have an AVP-lowering effect [ 10 , 64 , 65 ]. However, longer-term studies are needed to demonstrate whether lowering AVP through increased water intake is effective in maintaining metabolic health.

Lower AVP and renal water saving in chronic kidney disease (CKD)

The rationale for use of water as a treatment in CKD is based on its ability to suppress the secretion and thus the detrimental effects of AVP on the kidneys [ 71 , 72 ]. AVP increases renal hyperfiltration and renal plasma flow with its associated proteinuria, hypertension and renal scarring [ 73 , 74 ]. AVP antagonists reduce proteinuria, lower blood pressure and prevent renal injury. Water intake acts as an AVP antagonist, as shown by the experimental animal work of Bouby and Bankir in 1990 which demonstrated the therapeutic role of increased hydration in slowing progressive loss of kidney function [ 72 ].

Water intake and its relationship with AVP in patients with CKD is documented by various human observational studies assessing hydration as a potential therapy in CKD. However, there are inconsistencies in these studies regarding the possible benefits of increased water intake to slow and prevent CKD [ 75 , 76 , 77 , 78 , 79 ]. Briefly, cross-sectional studies in Australian and American cohorts have reported a kidney protective effect of higher fluid intake [ 76 ] and lower prevalence of CKD in participants reporting higher plain water intake, a beneficial effect not observed for any other type of beverage [ 77 ]. In contrast, a second prospective study analyzing longitudinal data of the same Australian cohort reported no significant association between total fluid intake and longitudinal loss of kidney function [ 78 ]. This apparent contradiction with the previous analysis may be due to the fact that plain water intake, a major driver of high fluid intake [ 80 ], was excluded from analysis. Finally, a 7-year longitudinal study of over 2000 Canadians that controlled for multiple baseline variables also demonstrated that higher urine volumes significantly predicted slower renal decline [ 79 ]. These observations are further strengthened by a longitudinal study of more than 2000 CKD patients with 15-year median follow-up demonstrating that those in the highest quartile of fluid intake had better survival outcomes than those in the lowest quartile [ 81 ].

To our knowledge there exists a single RCT on water intake in CKD prevention. In a six-week pilot study of 29 patients with stage 3 CKD, Clark et al. showed that an increased urine volume of 0.9 L was associated with a significant reduction in copeptin without any toxicity or measurable change in quality of life [ 82 , 83 ]. This pilot study led to the Water Intake Trial [ 84 ], a parallel-group RCT in which adults with stage 3 CKD and microalbuminuria were either coached to increase water intake by 1 to 1.5 L day −1 above their usual intake (high water intake (HWI) group), or to maintain usual water intake. The primary analysis at 1-year follow-up demonstrated that a 0.6-L increase in urine output in the HWI group versus the control group was associated with a small but significant reduction in copeptin, but not associated with a difference in albuminuria nor in estimated glomerular filtration rate (eGFR). However, this trial may have focused on the wrong population, as the majority of participants ingested approximately 2–3 L of fluid per day at baseline; consequently, the margin for improved hydration was small. Future RCTs should consider focusing on the role of increased hydration in low water drinkers with high copeptin levels and thus higher potential to respond to increased water intake, include more precise measures of renal function and possibly a longer follow-up.

Autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic disorder characterized by development and enlargement of multiple cysts in the kidney, leading to loss of renal function, hypertension, and renal failure in 50% of patients by the age of 60 [ 85 ]. The major sites of cyst development in ADPKD are the collecting ducts and distal nephrons, where cyclic adenosine monophosphate (cAMP) stimulates both epithelial cell proliferation and fluid secretion [ 86 ]. Since AVP is a strong activator of cAMP in these loci [ 87 , 88 ], the rate of progression of the disease is associated with its circulating concentration: a loss of urinary concentrating ability early in ADPKD is associated with a concomitant rise in AVP [ 89 , 90 , 91 , 92 , 93 ]. Further, preclinical studies demonstrate that ADPKD progression is slower in animals lacking AVP, and that in AVP knock-out animal models, desmopressin, a synthetic AVP analogue, accelerates disease progression [ 87 , 94 ].

Reducing AVP action represents a recent therapeutic target for patients with ADPKD, with two possible mechanisms: (1) blocking its receptors; more specifically the V2R in the collecting ducts; or (2) decreasing circulating AVP. Administration of vaptans, a class of nonpeptide AVP receptor antagonists, in particular tolvaptan, an oral selective antagonist of the V2R, decrease cAMP in epithelial cells of the collecting ducts and distal nephron [ 95 ]. A recent RCT reported inhibition of the action of AVP by tolvaptan significantly slows the rate of disease progression [ 96 ].

The suppression of AVP by increasing water intake could also slow renal cyst growth in ADPKD [ 87 , 88 , 94 , 96 , 97 ]. Rodent models of polycystic kidney disease have shown AVP suppression by increased water intake is associated with a significant renal-protective effect [ 87 ]. However, data available in humans are limited and conflicting. A positive effect of high water intake on ADPKD was observed in one post hoc analysis [ 98 ] and two short-term interventional trials [ 98 , 99 ] while a negative effect of high water intake was reported in a small observational cohort study [ 100 ] One large RCT is currently underway to determine the efficacy and safety of increasing water intake to prevent the progression of ADPKD over a 3-year period [ 101 ].

AVP, or the antidiuretic hormone, is most well-known for its central role in maintaining body water balance. However, AVP can also stimulate hepatic gluconeogenesis and glycogenolysis and can moderate glucose-regulating and corticotrophic hormones through its V1a and V1b receptors. The AVP-V2 receptor is also implicated in the pathophysiology of a particular form of kidney disease (ADPKD).

In epidemiological studies, higher circulating AVP, measured by its equimolar surrogate, copeptin, is associated both cross-sectionally and longitudinally with higher odds for kidney function decline, components of the metabolic syndrome, and incident T2DM.

Short-term intervention studies suggest that in individuals with higher AVP, increasing water intake can have an AVP-lowering effect. However, it is unclear whether lowering AVP through increased water intake will reduce disease risk.

Optimal hydration

If water intake may contribute to maintaining kidney and metabolic health, what would constitute optimal hydration and how much water should one consume?

Based on the evidence above, optimal hydration should result in excretion of a generous volume of dilute urine, sufficient to avoid chronic or sustained renal water saving and excess AVP secretion. Individual needs vary; nonetheless, the available data (Tables 1 , 2 ) provide a starting point for practical and evidence-based recommendations.

The first recommendation is that beyond replacing daily fluid losses, optimal hydration should be viewed as allowing the excretion of a sufficient urine volume to avoid urine concentration and supersaturation. Based on the evidence for fluid intake, urine volume, and kidney stones and UTI, it would appear reasonable to maintain a volume of excreted urine of 2 to 3 L per day. To account for other avenues of water loss (insensible, fecal [ 4 , 14 ]), achieving a urine volume of 2 to 3 L would require consuming a fluid volume slightly higher than the AIs currently proposed by EFSA [ 14 ], and approaching the IOM AIs [ 4 ]. We suggest that daily total water intake for healthy adults in a temperate climate , performing, at most, mild to moderate physical activity should be 2.5 to 3.5 L day −1 . While total water intake includes water from both food and fluids, plain water is the only fluid the body needs. Plain water and other healthy beverages should make up the bulk of daily intake. A practical, evidence-based scoring tool for evaluating healthy beverage choices has been proposed by Duffey et al. [ 102 ].

The second recommendation, for healthy individuals as well as in those with metabolic dysfunction, is to drink enough to reduce excessive AVP secretion as this may be beneficial for the kidney and reduce metabolic risk. This is especially relevant for individuals who may be underhydrated [ 103 ], with low 24 h urine volume or high urine concentration suggestive of AVP secretion linked to insufficient water intake. While higher circulating AVP is associated with increased disease risk, to date there is insufficient data to suggest a level of copeptin which may be appropriate to target for risk reduction. However, the use of urinary biomarkers of hydration such as osmolality can provide useful information reflecting urine concentrating and diluting mechanisms and overall antidiuretic activity. Multiple authors have proposed cut-offs representing de- or hypohydration for several urinary and plasma biomarkers (Fig.  1 ), conversely, suggestions for optimal hydration are infrequently provided [ 28 , 104 , 105 , 106 , 107 , 108 , 109 , 110 , 111 , 112 , 113 , 114 , 115 , 116 ]. Several years ago a cutoff of 500 mOsm kg −1 was proposed as a reasonable target for optimal hydration, based on retrospective analyses of existing data [ 109 ] indicating that this cut-off would represent sufficient water intake to produce adequate urine volume with respect to kidney health risk, and reduce antidiuretic effort and circulating AVP. Today, several RCTs have demonstrated that lowering 24 h urine osmolality to approach 500 mOsm kg −1 or below can reduce circulating copeptin [ 10 , 64 , 65 ] as well as improve metabolic markers [ 66 ] and reduce UTI incidence [ 42 ]. For clinician or home use, maintaining a urine specific gravity of less than 1.013, or a urine color of 3 or below [ 108 ] on an eight-point color scale [ 107 ], or a 24 h void frequency of at least 5 to 7 voids daily [ 114 , 115 ] are suggestive of a fluid intake sufficient to achieve optimal hydration (Fig.  1 ). As color and void frequency are accessible without specific laboratory instruments, they may be used by the general population for daily hydration awareness.

Terminology and associated cut-off values for common biomarkers of hydration. * Defined as ‘impending dehydration’. † In the original text, these values are described as limits for euhydration (e.g., POsm < 290, UOsm < 700). For clarity we have positioned these values as limits for dehydration (e.g., POsm ≥ 290, UOsm ≥ 700) in order to avoid the interpretation that these values were limits for insufficient hydration. ‡ Decision level for 95% probability of dehydration. § Approximate range of plasma copeptin in bottom quartile or other reference interval (lowest risk for kidney or cardiometabolic disease)—see Table 2 . || Approximate range of plasma copeptin for increased risk for kidney or cardiometabolic disease—see Table 2

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A randomized, double-blind water taste test to evaluate the equivalence of taste between tap water and filtered water in the Taipei metropolis

• Jing-Rong Jhuang 1 ,
• Wen-Chung Lee 1 , 2 &
• Chang-Chuan Chan 2 , 3  

Scientific Reports volume  10 , Article number:  13387 ( 2020 ) Cite this article

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• Energy and society
• Environmental social sciences
• Psychology and behaviour
• Sustainability

High water quality and sufficient water availability are the main concerns of water users. Promoting the efficient use of tap water can contribute to sustainable drinking water management and progress towards Sustainable Development Goals. In many metropolises, water suppliers treat municipal water with appropriate treatment processes and well-maintained distribution infrastructure. Under this circumstance, it is acceptable that municipal water can be a source of drinking water. The presence of residual chlorine in tap water, connected to municipal water supply, inactivates pathogenic microorganisms and prevents recontamination. However, adding chlorine to tap water may affect the organoleptic properties of drinking water. On the other hand, the use of point-of-use (POU) water dispensers, which provides an additional treatment step on tap water, is not energy-efficient. A randomized, double-blind water taste test was conducted in the Taipei metropolis to assess whether tap water from public drinking fountains and filtered water from POU water dispensers have similar organoleptic properties. An odds ratio (OR) and the area under the receiver operating characteristic curve (AUC) were used to measure the participants’ ability to distinguish between the two water varieties. A five-region hypothesis test was conducted to test the OR, and a 95% bootstrap confidence interval of the AUC was calculated. The results of the study showed that the 95% five-region confidence interval of OR equal to (0.5, 1.49), and the 95% bootstrap confidence interval of AUC equal to (0.42, 0.56). These results implied that people in the Taipei metropolis could not distinguish between tap water and filtered water. It is recommended that more drinking fountains be installed and maintained fully functional and clean to achieve excellence in tap water access.

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Introduction

High water quality and sufficient water availability are the main concerns of water users. Water utilities must treat and supply water to meet specific water quality standards. In many metropolises, water suppliers treat municipal water with appropriate treatment processes and well-maintained distribution infrastructure, ensuring high-quality municipal water and sufficient water availability. Under this circumstance, it is acceptable that municipal water can be a source of drinking water. Tap water, connected to municipal water supply, is a common and efficient source of drinking water. The presence of residual chlorine in tap water inactivates pathogenic microorganisms that cause waterborne diseases 1 , 2 and prevents recontamination during storage or transportation 3 . The World Health Organization (WHO) provided guidelines for drinking-water quality that residual chlorine levels in tap water should be maintained at concentrations of 0.2–5 mg/L 4 .

The United Nations General Assembly has proposed Sustainable Development Goals (SDGs) to achieve a more sustainable future by 2030 5 . Among the 17 goals, SDG 6 addresses the availability and sustainable management of water and sanitation. Promoting the efficient use of tap water can contribute to sustainable drinking water management and progress towards SDG 6. However, adding chlorine to tap water exhibits effects on the taste and odor of drinking water, which can reduce people’s preference for tap water 6 , 7 , 8 and impede acceptance and sustainability of the water quality intervention 9 . The point-of-use (POU) water dispenser, which works by connecting to municipal water supply and drawing water from the waterline that is already in place, provides an additional treatment step on tap water. The application of replaceable filter in a POU water dispenser can improve the organoleptic quality of tap water 10 , 11 , 12 by removing chlorine, solid precipitates, discoloration, unpleasant scent. A POU water dispenser has the option to provide hot or cold water on command. And the predominant demand for energy in such water dispensing systems is from the heating or cooling of water before consumption. In Taiwan, the total energy consumed by 5.48 million water dispensers was 3.15 billion kWh per year 13 . The water dispenser was also the fifth electricity-consuming household appliances in Taiwan 14 . High energy consumption can complicate the achievement of SDG 7, which represents affordable and sustainable energy. Also, in a city, tap water and water from POU water dispensers are connected to the municipal water supply, from the same water source, water treatment processes, and distribution piping system. For sustainability in water supply, it is unnecessary to treat water that is already of good quality at the end-user point. Therefore, a better understanding of the public perception and preferences of tap water can contribute to improvements in water management, consumer services, and sustainability.

Municipal water in Taipei city meets drinking-water standards in WHO, USA, Europe, and Japan 15 . The perception and preferences of tap water are still unknown in the Taipei metropolis. The study aimed to investigate whether tap water has organoleptic properties similar to filtered water from POU water dispensers. It was expected that people could not distinguish the two water varieties such that there is no advantage in treating water that is already of good quality at the end-user point.

Material and methods

Study design and randomization.

A randomized, double-blind water taste test was designed (Fig.  1 ). Water from a public drinking fountain (tap water) and cold water from a POU water dispenser (filtered water) were obtained and were let stand for an hour at room temperature. A thermometer was used to ensure that the temperature was at 25 °C for both the water varieties. Paper cups with the same appearance were prepared. For each paper cup, a random decimal number between 0 and 1 was generated by using a computer, and the cup was assigned to the tap-water group if the number was ≥ 0.5 and to the filtered-water group if the number was < 0.5. A fixed and identical amount (200 ml) of the appropriate water variety was poured into each paper cup according to the group to which it was assigned. A sealed letter containing the group information was attached to the outside of each paper cup.

Procedure for the water taste test.

One-on-one interviews were conducted. The interviewer, who was not involved in water sample preparation, first told the participant that residual chlorine exists in tap water from public drinking fountains but not in filtered water from POU water dispensers. Next, the participant was invited to taste a cup of water. (Participants who refuse to drink the water were excluded.) Neither the interviewer nor the participant knew which water variety was served in the cup, except that it could be tap water or filtered water with equal probability. The interviewer then instructed the participant to guess the water variety. After the guess, the participant opened the sealed letter to reveal the correct answer.

Measures of distinguishability

The participants’ ability to distinguish between the two water varieties was measured using an odds ratio (OR) 16 as follows:

where Se (sensitivity) and Sp (specificity) represent the probabilities of guessing the correct answer in the tap-water group and the filtered-water group, respectively. When obtaining OR = 1, it indicated that the proportions of the participants guessing “tap water” were equal in the two groups; that is, the participants could not distinguish between the two water varieties by any means. When obtaining OR > 1, it indicated that the proportion of the participants replying “tap water” was higher in the tap-water group than in the filtered-water group. The higher the OR, the stronger the participants’ abilities to distinguish between the water varieties. When obtaining OR < 1, it indicated that the participants were not only unable to distinguish between the water varieties but also tended to guess incorrectly. The smaller the OR, the stronger the tendency to guess incorrectly.

The participants' ability to distinguish between the water samples was also measured using the area under the receiver operating characteristic curve (AUC) 17 :

An AUC of 0.5 indicated that the participants could not distinguish the two water varieties by any means. An AUC of > 0.5 indicated that the participants could distinguish between the water varieties, and the higher the value, the stronger was their ability to distinguish between the water varieties. An AUC of < 0.5 indicated that the participants could not distinguish between the water varieties, and the smaller the value, the stronger was the tendency to guess incorrectly.

Statistical analyses

A newly proposed five-region hypothesis test 18 was conducted to test the OR. The five regions were defined as \(\hbox{OR}>2\) (a recognizable ability to distinguish between the water varieties; we also consider a more lenient criterion of \(\hbox{OR}>1.5\) for this category), \(1< \hbox{OR} \le 2\) (a negligible ability to distinguish between the water varieties; also a stricter criterion of \(1<\hbox{OR} \le 1.5\) for this category), \(\hbox{OR}=1\) (no ability to distinguish between the water varieties), \(0.5\le \hbox{OR} <1\) (a weak tendency to guess incorrectly), and \(\hbox{OR}<0.5\) (a strong tendency to guess incorrectly). The 95% five-region confidence interval 18 of the OR was also calculated. To conclude 18 that the participants have no recognizable ability to distinguish between the two water varieties ( \(\hbox{OR}\le 2\) ), at least 207 participants were required to be recruited to achieve a power of 80% at a significance level of 0.05. Furthermore, we generated 10,000 bootstrap samples and calculated a 95% bootstrap confidence interval 19 of the AUC. All analyses were performed with R version 3.5.2 20 .

Consent for publication

Not applicable.

Ethical approval and consent to participate

Study site, participants, and data collection, water supply and sanitation.

There are two state-owned water utilities in Taiwan; Taiwan Water Corporation provides water supply to Taiwan except for the Taipei metropolis, whereas the Taipei Water Department is exclusively responsible for supplying water to the Taipei metropolis. The primary source of raw water is Xindian Creek, representing 97% of the total raw water supply in the Taipei metropolis. Qingtan Dam and Zhitan Dam are in operation at the Xindian Creek. The two water intake units take in 1.08 (Qingtan Dam) and 2.70 (Zhitan Dam) million cubic meters of raw water daily, respectively, which are conveyed with gravity via tunnels to the Zhangxingm, Gongguan, or Zhitan Purification Plants for treatment. The treatment process comprises testing, applying chemical disinfectants, coagulation, mixing, sedimentation, and filtering. Wastes discharged from the water purification process, including settled flocculating waste and filter backwash waste, are sent to Zhitan or Gongguan purification plants to process.

Water pipeline network with a caliber ranging from 75 to 3,400 mm that add up to a total length over 3,000 km has been placed in the Taipei metropolis. A water supply monitoring and control system was developed in 1991 for better control of pressure changes and leakage in the distribution system, flexible adjustment of water supplies, and early detection and prevention of accidents. Due to the requirement for adjusting the delivery of treated water to meet demand adequately, 92 distribution basins have been set up. Also, 60 pumping stations have been set up at appropriate locations to enable water supply to reach the farthest ends of the distribution piping system, particularly those at high altitudes.

Some measures have been implemented in the Taipei metropolis to meet the goal of sustainable water resources. Automatic Water Quality Monitoring System was established in 1985 to monitor the water quality in the raw water intakes, the treatment process at its purification plants, and the distribution system. To enhance water availability for drinking, approximately 280 public drinking fountains that provide clean and safe tap water have been installed 21 . Also, a QR code that provides water users with updated information about the quality of tap water (turbidity, pH, and residual chlorine) was equipped on each public drinking fountain.

Participants and data collection

The study protocol was approved by the College of Public Health, National Taiwan University (NTU), where the study was conducted (in the Zhongzheng District of the Taipei metropolis). All methods were carried out following the guidelines and regulations of NTU. Students and teaching faculty members of the College of Public Health, NTU, were recruited for the study. Informed consent was obtained from all the participants. The study period was from March to April 2018. The primary source of drinking water in this study site (NTU Public Health Building) is the POU water dispensers. Currently, a public drinking fountain has been set up, which can be another choice for the students and the teaching faculty members to drink. The participants were invited to attend the water taste test in a small room, and after the test, they can win a gift. Eight well-trained interviewers collected data from the participants. The collected variables include gender and position of each participant, whether or not he (or she) had drunk cold water from water dispensers in the previous month and had drunk water from drinking fountains before, the water variety he (or she) guessed, the actual water variety he (or she) drank, and his (or her) preference for tap water from drinking fountains.

A total of 278 participants took part in the test; 139 were randomly assigned to the tap-water group and the remaining to the filtered-water group. Table 1 presents the baseline characteristics of the participants. The two groups did not differ significantly in their characteristics. Table 2 presents the results of the water analysis of the two water varieties. The water qualities of the two water varieties were similar except for total residual chlorine and pH.

Table 3 presents the results of the water taste test. A total of 216 participants (77.7%) replied, “tap water.” The numbers of the participants who replied, “tap water,” were 106 (76.3%) and 110 (79.1%) in the tap-water group and the filtered-water group, respectively. The Se, Sp, and OR estimates were 0.76, 0.21, and 0.85, respectively. Table 4 presents the results of the analysis of the participants’ abilities to distinguish between the two water varieties. The 95% five-region confidence interval of the OR for all the participants was (0.5, 1.49), excluding \(\hbox{OR}>2\) (and also \(\hbox{OR}>1.5\) ) and \(\hbox{OR}<0.5\) entirely; the p-value for the \(\hbox{OR}>2\) hypothesis (a recognizable ability to distinguish between the water varieties) was 0.01 (0.02 for the \(\hbox{OR}>1.5\) hypothesis), and the p-value for the \(\hbox{OR}<0.5\) hypothesis (a strong tendency to guess incorrectly) was 0.03. These results indicated that the participants could not distinguish between the two water varieties and that the indistinguishability of the water varieties was statistically significant. Besides, the estimate of the AUC was 0.49, with a 95% bootstrap confidence interval of (0.42, 0.56), which encompassed the null value of 0.5.

A subgroup analysis (Table 4 ) was also performed. The value of \(\hbox{OR}>2\) was rejected in male participants, female participants, students, and those who have not drunk cold water from water dispensers in the previous month. The values of \(\hbox{OR}>2\) and \(\hbox{OR}<0.5\) were rejected in those who have drunk cold water from water dispensers in the previous month and those who have not drunk water from drinking fountains before. However, because of the small sample size, the power was insufficient to reject \(\hbox{OR}>2\) or \(\hbox{OR}<0.5\) in the faculty members and those who have drunk water from drinking water fountains before. The 95% bootstrap confidence intervals of the AUC encompassed 0.5 in all subgroups.

A randomized, double-blind water taste test was performed, and the results showed that the participants could not distinguish between tap water and filtered water. The participants (after the water taste test) were asked whether they were willing to drink from drinking fountains if they could choose to drink from POU water dispensers. Most of the participants (252, 90.6%) provided affirmative responses. Based on these findings, in general, it is unnecessary to treat municipal water in the Taipei metropolis at the end-user point.

In the water taste test, the participants were being told from the outset that the water to be drunk had a 50:50 chance of being from a drinking fountain and a water dispenser. However, the participants had a biased belief that the water was more likely to be from a drinking fountain than a water dispenser (78:22), perhaps because they tend to associate the taste of water dispensers with cold or hot water rather than room temperature water as in this study. Nevertheless, the OR, the primary measure in the study, is impervious to such a bias. The study aimed to prove the equivalence of the two water varieties on taste. A conventional hypothesis test can only prove nonequivalence; we cannot conclude that the taste of the two water varieties is equivalent when the test result is nonsignificant. By contrast, the five-region hypothesis test we used in this study is a legitimate test to conclude that the OR significantly fell into a pre-specified equivalence region (from 0.5 to 2.0; or from 0.5 to 1.5) of the two water varieties, which indicated the taste of the water varieties is statistically equivalent 22 .

In a group interview, participants may discuss the water tastes; therefore, in this study, a one-on-one interview was adopted to avoid possible contamination biases. In this study, students or teaching faculty members who had been smoking or eating within one hour before the water taste test were not excluded. However, the randomization was conducted to control any possible bias this may induce. In most settings, we believed that people would drink water from an easily accessible source to quench their thirst but would not drink deliberately from two different sources at the same time merely to compare the tastes. Therefore, each participant tasted only one water variety, unlike other studies, which let each participant taste no less than two water varieties 23 , 24 . In general, information about the characteristics of water samples is not to be given to tasters in a sensory evaluation test. In this study, information about residual chlorine exists in tap water was told before the water taste test because most of the participants have not drunk water from drinking fountains before, and the preference for tap water in the study site was unknown before the study.

Information about the chemical quality of the two water varieties would be crucial to evaluate the study results. According to previous studies, the taste detection thresholds for residual chlorine has an extensive regional variation, from 0.17 to 0.71 mg/L 4 , 24 , 25 . The residual chlorine levels of tap water ranged from 0.27 to 0.39 mg/L during the study. However, the two water varieties were allowed to stand for an hour at room temperature before the water taste test (for ensuring proper control). This procedure may allow some residual chlorine in tap water to dissipate and may have rendered the two water varieties more challenging to distinguish. An extreme pH value on filtered water was observed on one particular day in the study period, which may also influence the study results. A previous study 26 indicated that it is difficult to discriminate the two water varieties when the difference in total dissolved solids (TDS) among the two is lower than 150 mg/L. In this study, there was a minor difference (about 10 mg/L) in TDS among the two water varieties during the study period. Additionally, minerals are correlated with the taste of water 27 but were not measured in this study.

Bottled water, which is also an alternative to tap water 6 , 7 , 27 , 28 , 29 , was not compared in this study because whether consumers could perceive the presence of residual chlorine in drinking water was mainly concerned. Water samples in the study were only collected from a POU water dispenser and a public drinking fountain. Further studies can be conducted to validate our findings in other locations in the Taipei metropolis (internal validation) or other cities having similar water sources, treatment processes, and distribution piping systems (external validation). The study results could not be generalized and extrapolated to other water varieties with medium or high TDS or to consumers who are more sensitive to the residual chlorine level, for example, French consumers 25 , bottled water drinkers 25 , or professional water sommeliers.

Although a POU water dispenser can provide clean and safe drinking water to meet SDG 6, high energy consumption constitutes obstacles in achieving SDG 7 (affordable and clean energy). This problem exhibits a trade-off between SDG 6 and SDG 7 30 , 31 . By contrast, drinking tap water improves energy efficiency. In locations where tap water has acceptable quality at the end-user point, it is recommended the use of tap water for drinking to achieve the synergistic development of SDG 6 and SDG 7 by providing clean water with affordable energy. To drink hot or cold water, using kettle heaters and refrigerators are more energy-efficient than using water dispensers; the average electricity consumption by kettle heaters (14.38 kWh per month per household 32 ) is lower than that by water dispensers (26.00 kWh per month per household 14 ), and refrigerators are already in use in many households in Taiwan.

Conclusion and perspectives

The study results concluded that people in the Taipei metropolis could not distinguish between tap water and filtered water. It is recommended that more drinking fountains be installed and maintained fully functional and clean 33 , 34 to achieve excellence in tap water access. POU water dispensers with functions of either heating or cooling water managed by the government can be uninstalled or replaced with drinking fountains. Public education toward more tap water use should be implemented. Furthermore, risk indices 35 for assessing the water supply systems should be determined to prevent substantial water quality deterioration. For achieving sustainable water management, we suggest using reclaimed water 36 , 37 , 38 to balance water supply and demand.

Data availability

Data collected from the water taste test and R code for statistical analysis are available at https://github.com/yoyo830303/water-analysis . The Taipei Water Department provided data about the water quality analyses of the two water varieties.

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Acknowledgments

We thank the reviewers for their feedback, which helped to improve the manuscript quality. We would like to acknowledge Hua-Shan Shi, Mei-Ku Chen, Jui-Min Hsia, Jing-Syuan Zeng, Wei-Cheng Tsai, Shih-Hsiang Liao, Ching-Hsiang Chang, Wan-Chu Lin and I-Hsin Chang for their assistance with collecting data. This study was supported by grants from the Ministry of Science and Technology in Taiwan (MOST 105-2314-B-002-049-MY3, MOST 104-2314-B-002-118-MY3, MOST 108-2314-B-002-127-MY3, and MOST 108-3017-F-002-001), and the Population Health Research Center from the Featured Areas Research Center Program within the framework of the Higher Education Sprout Project by the Ministry of Education in Taiwan (NTU-109L900308). No additional external funding was received for this study. The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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Contributions

W.-C.L. and J.-R.J. designed the study. J.-R.J. prepared the photograph in Fig.  1 , collected the data, conducted the statistical analysis and drafted the paper. Wen-Chung Lee and C.-C.C. supervised the study and wrote the paper. W.-C.L. and C.-C.C. are the guarantors. The corresponding authors attest that all listed authors meet authorship criteria and that no others meeting the criteria have been omitted.

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Jhuang, JR., Lee, WC. & Chan, CC. A randomized, double-blind water taste test to evaluate the equivalence of taste between tap water and filtered water in the Taipei metropolis. Sci Rep 10 , 13387 (2020). https://doi.org/10.1038/s41598-020-70272-y

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Hydration status moderates the effects of drinking water on children's cognitive performance

Affiliations.

• 1 University of California, Davis, Davis, CA, USA.
• 2 Nestlé Research Centre, Nestec Ltd, Switzerland.
• 3 University of California, Davis, Davis, CA, USA. Electronic address: [email protected].
• PMID: 26271221
• DOI: 10.1016/j.appet.2015.08.006

Changes in hydration status throughout the day may affect cognitive performance with implications for learning success in the classroom. Our study tested the hypothesis that the benefit of drinking water on working memory and attention depends upon children's hydration status and renal response to water intake. Fifty-two children aged 9-12 years old were tested under two experimental conditions. The treatment session (Water session) consisted of a standard breakfast with 200 ml water, a baseline test, consumption of 750 ml of water over a period of two hours and subsequently retested. No water was provided after breakfast during the control session. Changes in hydration were assessed via urine samples. Cognitive testing consisted of digit span, pair cancellation, and delayed match to sample tasks. Children who exhibited smaller decreases in urine osmolality following water intake performed significantly better on the water day compared to the control day on a digit-span task and pair-cancellation task. Children who exhibited larger decreases in urine osmolality following water intake performed better on the control day compared to the water day on the digit-span task and pair-cancellation task. These results suggest that focusing on adequate hydration over time may be key for cognitive enhancement.

Keywords: Attention; Children; Hydration; Urine osmolality; Working memory.

Copyright © 2015 Elsevier Ltd. All rights reserved.

Publication types

• Controlled Clinical Trial
• Research Support, Non-U.S. Gov't
• Attention / physiology*
• Cognition / physiology*
• Dehydration / physiopathology
• Dehydration / psychology*
• Drinking / physiology*
• Drinking Water / administration & dosage*
• Kidney / physiology*
• Memory, Short-Term / physiology*
• Osmolar Concentration
• Water-Electrolyte Balance
• Drinking Water

3. Generate Hypotheses

Developing a hypothesis regarding the cause of the outbreak is often challenging and is a crucial step in the outbreak investigation.

Many pathogens that cause waterborne diseases can also be transmitted by contaminated food or by contact with an infected person or animal. When looking for the source of the illness, investigators first need to decide on the likely mode(s) of transmission. The identified pathogen, where ill persons live, or the age of the patients may suggest a particular mode of transmission and could help identify a specific source. Hypothesis generation should be considered an iterative process in which possible explanations are continually refined or refuted.

When exposure to water is suspected as the source of contamination, public health officials interview ill cases to determine water exposures in the days or weeks prior to onset of illness. These interviews are called “hypothesis-generating interviews.”  Interviews can either use a standardized questionnaire (e.g., “shotgun” questionnaire), or they can be open-ended. Standardized interviews include a set of questions used by public health officials to interview ill people during outbreak investigations.  Open-ended interviews are not standardized and do not provide concrete exposures for analysis. Interviews will focus on activities and experiences that occurred during the pathogen’s incubation period—the time it takes to get sick after exposure to the contaminated water. A table of common waterborne pathogens and their incubation period is listed in the Appendices .

Based on all the information gathered, the investigators make a hypothesis about the likely source of the outbreak. If they are not able to develop a hypothesis, investigators can return to intensive, open-ended interviews or utilize a different set of standardized questions to develop clues to the outbreak source. Clues to the outbreak source might come from ill persons with few exposure opportunities or from interviewing cohorts (e.g., family groups or sports teams) within the larger outbreak population.

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Science in School

What are you drinking tap water versus bottled water teach article.

Author(s): Daniela Bergamotti, Paola Semeghini

Which is better: tap or bottled water? Try these activities based on simple analyses, a debate, and a blind tasting to learn about drinking water and encourage sustainable habits.

Water management is crucial to sustainable development, because clean freshwater is essential to human health and well-being. Many prefer bottled water over tap water, but this has a high environmental impact in terms of waste production and pollutants. Many beliefs are related to preconceived ideas rather than to actual experiences or product characteristics: in most EU countries, tap water is controlled, safe to drink, and usually tastes good.

These activities aim to determine students’ views on the topic and influence changes in water consumption and perception. They will increase their knowledge and trust of distributed drinking water and consider the overconsumption of plastic bottled water.

Curriculum links

• chemistry topics: pH, acids and basis (Lewis theory), group 2 metal ions, complexation reactions, solution preparation and concentration, titration technique and principle of the method, pH indicators;
• earth sciences: composition of limestone sedimentary rocks;
• biology: water as a source of mineral salts, physiological effects, osmotic pressure in cells.

We devised the following activities for students aged 16–19. They are also suitable for ages 14–16 if there is less emphasis on titration methods and chemical reactions.

Activity 1: Introduction to drinking water

Firstly, students are given some background information on types of drinking water and invited to do some research on the drinking water in their area.

This activity involves 1 hour of introduction and 2 hours of homework.

• Introduction on water management ( Drinking water infosheet )
• Internet access for research
• Information on/plan of the local water system and water quality (guided visits to water plants are strongly recommended to acquire on-site knowledge of distributed water)
• To-do list ( Local water task sheet )
• Presentation evaluation rubric
• After an introduction on water management and uses (1 h), the students are divided, depending on where they live, into groups of two to four.
• Based on water certificates of analysis (available from the local water utility website) and school science texts, they should prepare a short PowerPoint presentation, following the to-do list on the Local water task sheet . This should include a plan of the area, with a description of the water origin (spring, ground water, or surface water) and its path from source to tap.
• A comparison of the hardness values in different areas influenced by geological features can be made, if applicable.
• The students should assess the values indicated on a water certificate of analysis (e.g., pH, nitrogen content, hardness, etc.) and describe the possible health risks associated with noncompliance.
• The presentations can be marked based on the presentation evaluation rubric .

Activity 2: A debate on tap water versus bottled water

To explore different types of drinking waters and the consequences of our consumption habits, students conduct research and then run a class debate on tap water versus bottled water.

As an alternative, the debate can be left until after Activities 3 and 4, as a consolidating activity at the end.

This activity takes about 3 hours: 1 hour of introduction and research, 1 hour to prepare arguments, and 1 hour for the debate.

• Materials from reliable resources
• Parameters for discussion and debate rules ( Debate task sheet )
• Debate evaluation rubric
• 1 projector or digital board
• Students should be provided with articles and web materials from official sites or publications (e.g., WHO guidelines, Ministry of Health guidelines, data published on the local water company’s website, medical and research associations, articles on environmental issues) that they can integrate with other sources considered to be reliable. See the supporting material for suggested parameters to consider.
• The class is divided into two teams (chosen at random), each supporting one of the motions (tap water or bottled water). Each student should take one parameter (see the Debate task sheet ; make sure all are covered), examine the sources, do their own research, and prepare two sentences to argue their case and one sentence to argue against possible points made by the opposition.
• In the classroom, each team should prepare a list of arguments and counterarguments to ensure that all participants can provide a contribution to the discussion.
• Before the debate, the teacher checks that every argument is based on reliable sources and includes significant and well-documented data or scientific information.
• In the debate, the sides speak in turn. All participants must make a statement. Each speaker has a specified amount of time to speak (approx. 2 minutes) and present arguments and counterarguments (e.g., tap water can taste (smell) like chlorine – to remove chlorine, place a jug of water in the fridge for a few hours before drinking it).

The argumentation skills of each participant, in terms of presentation and content, can be evaluated using the debate evaluation rubric .

After the debate, the class can discuss what they’ve learned. Invite students to share things they didn’t know before or found surprising. Will this affect their drinking habits?

Activity 3: Determination of total hardness in water

Students can analyze their home/school tap water or marketed bottled waters.

For tap water, they should compare the analytical results with the certificates of analysis provided by the local water company; for bottled water, they should compare them with those shown on the labels.

The determination of the total hardness in water is made by titration with ethylenediamine tetraacetic acid (EDTA), which forms colourless stable complexes with Ca 2+ and Mg 2+ ions at pH = 9–10. These ions are naturally present in water due to minerals that dissolve as water passes through soil and rocks.

To maintain the pH of the solution at 9–10, a buffer solution (NH 4 Cl + NH 4 OH) is used. The indicator Eriochrome Black T (EBT) changes colour when these two ions are completely complexed by EDTA.

In addition to the hardness test described here, other tests can be proposed, depending on time and instrument availability, such as:

• calcium and magnesium ion concentrations (atomic absorption)
• calcium salts (flame test)
• bicarbonate concentration (water alkalinity titration)
• microbial analysis of total coliforms (faecal contaminants – reference value: 0 colony forming units (CFU) per ml)

This activity takes about 2 hours. Time is also needed for preparing solutions and equipment (1 h; this can be done by the teacher or technician).

Safety notes

Wear lab coat and gloves

Materials (per group)

• 50 ml burette (+ support)
• 100 ml graduated cylinder
• 250 ml conical flask
• 100 ml beaker
• Glass funnel
• 0.01 M sodium EDTA solution
• Stainless-steel spatula
• Buffer solution, pH 10 (NH 4 Cl + NH 4 OH)
• The provided Water-hardness scale
• Split students into groups of two to four. Assign each group a water sample (tap, distilled, filtered, bottled).
• Fill the burette with 0.01 M EDTA sodium solution (titrant).
• Measure 100 ml of water (sample) into a 250 ml conical flask.
• Add a small amount (a few crystals) of EBT powder (indicator): the solution in the conical flask will turn a rose–violet colour.
• Titrate with sodium EDTA solution until the colour changes to light blue without violet shades.

• Measure the volume of titrant added and take note of it.
• Repeat at least three times and calculate the average volume of titrant.
• What do you observe when the indicator is added to the water + buffer solution?
• What do you observe when a small amount of EDTA is added to the solution? (The colour does not change; it forms colourless stable complexes with Ca 2+ and Mg 2+ ions, which are naturally present in water.)
• Why does the solution turn blue when an extra volume of EDTA is added? (Because all Ca 2+ and Mg 2+ ions have been complexed by EDTA.)
• Calculate the total hardness in French degrees (F°; not to be confused with degrees Fahrenheit!) as mg/l of calcium carbonate (CaCO 3 ) according to the following formula:

1 ml sodium EDTA solution (0.01 M) = 1F° = 10 mg/l CaCO 3

• Classify water as very hard, hard, moderately hard, medium, soft, or very soft: values can change according to local laws, but should be between 10 and 50F°.
• Compare the value with that shown on the label (bottled water) or certificate of analysis from the local water company (tap water).

Units of water hardness

There are a number of different common official measurement units for hardness: [ 1 ]

– Parts per million (ppm) is usually defined as 1 mg/l CaCO 3 . It is equivalent to mg/l without a specified chemical compound.

– French degree (°F or f): 10 ppm or mg/l CaCO 3 . Lowercase f is often used to prevent confusion with degrees Fahrenheit.

– Degree of general hardness (dGH) or German degree (°dH, deutsche Härte): 10 mg/l CaO, equivalent to 17.85 ppm or mg/L CaCO 3 .

– Clark degree (°Clark) or English degrees (°e or e): one grain (64.8 mg) of CaCO 3 per imperial gallon (4.54609 litres) of water, equivalent to 14.254 ppm or mg/l CaCO 3 .

– US degree (gr/gal): a grain CaCO 3 /gal (US gallon = 3.78541 litres), equivalent to 17.118 ppm or mg/L CaCO 3 .

• Does your result match with theoretical values?
• If not, what could be the reasons (e.g., old or ill-maintained pipes, presence of a water softener)?
• If yes, could you form a hypothesis about the origin of water under survey (bottled or distributed water, surface or groundwater, geological characteristics of the catchment area)?
• How do you measure hardness in French degrees? (By measuring the volume in ml of EDTA added under the method conditions.)
• How do you measure hardness in mg/l expressed as CaCO 3 ? (By multiplying the value in French degrees by 10.)

Activity 4: Blind tasting of water

Research shows that tap water is just as safe as bottled water and is often not significantly different in taste. Tap water is generally a better option, since it has a much lower environmental impact and costs considerably less.

This activity is useful to work out common perceptions around the topic and discuss water-drinking habits. The duration depends on the number of participants in the blind-tasting session (at least 50 are required for statistically significant results).

Bottled waters should be selected to include a highly advertised luxury brand, to show how price and advertising do not have a significant impact on taste preferences.

If the tap water is very hard and/or does not taste so good, it can be replaced with filtered tap water.

• 3 glass bottles/jugs
• Paper or compostable coffee cups
• 2 types of bottled water (hardness: 4–8 °F and 20–25 °F)
• Paper for labelling each bottle/jug
• Blind-tasting questionnaire
• Encourage the students to come up with their own questions for the questionnaire. The provided questionnaire can be used as a template.
• Fill up the bottles: each bottle should be filled with a different type of water.
• Line up the bottles and arrange the cups on a table.
• Place a numbered/coloured slip of paper next to each bottle.
• Have someone who is not participating in the test pour the different types of water into three separate cups for each participant. Ideally the cups should be labelled with the same number/colour as the corresponding bottle.
• The participants should take a sip from each cup and fill in the questionnaire to express their perceptions of the three waters included in the taste test, answering the following possible questions: What type of water do you think it is? How would you describe its taste? Do you like it? Can you taste any flavourings? What was your favourite water? Why?

The tasting results can be statistically processed (e.g., test results in terms of number of voters, % assigned to each type of water (pie chart), and choice motivations) and collected in a poster or digital presentation.

They can be shared and made public through the school website, social media, and/or a poster exhibition encouraging the benefits of sustainable drinking habits.

In many blind taste tests, participants find bottled water to be indistinguishable from tap water, and tap water is often the favourite one, showing that many beliefs are related to preconceived ideas rather than to actual experiences or product characteristics.

The MULTIPLIERS project

This teaching and learning activity was developed as part of the MULTIPLIERS Horizon 2020 project by Iren, an Italian multiutility company and one of the MULTIPLIERS partners, through its educational department Eduiren and in cooperation with the Pascal upper secondary school in Reggio Emilia.

MULTIPLIERS promotes open schooling across Europe to make science more meaningful and directly relevant to real-world challenges. By connecting students with universities, informal education providers, museums, local associations, industry, civil society, policymakers, media, and other actors in authentic learning settings, the project promotes competence development in socioscientific issues that have a direct impact at the local level and beyond. The ultimate goal is to foster social transformation by enabling students to act as “knowledge multipliers”, sharing their learnings and findings with their wider communities.

MULTIPLIERS has received funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement No. 101006255.

Learn more about the project: https://multipliers-project.org/

[1] The Wikipedia entry on how to measure hard water: https://en.wikipedia.org/wiki/Hard_water#Measurement

• Learn how to spot pseudoscientific fake news in the media: Domenici V (2022) Fake news in chemistry and how to deal with it . Science in School 59 .
• Read about the impacts of meat consumption and the development of lab-grown substitutes: Noble M (2023) From Petri dish to plate: the journey of cultivated meat . Science in School 63 .
• Read an article about the environmental effects of food packaging: Barlow C (2022) Plastic food packaging: simply awful, or is it more complicated? Science in School 56 .
• Explore the water footprints of the foods we eat: Kelly S (2020) Do you know your water footprint? Science in School 50 .
• Teach about freshwater with these low-cost experiments: Realdon G et al. (2021) Watery world – hands-on experiments from Earthlearningidea . Science in School 54 .
• Investigate the properties of so-called superfoods: Frerichs N, Ahmad S (2020) Are ‘superfoods’ really so super? Science in School 49 : 38–42.
• Teach about water quality and analysis: Al-Benna S (2014) Become a water quality analyst . Science in School 29 : 35–40.

Cutting-edge science: related EIROforum research

Seed extracts from the Moringa tree have been used for centuries to help purify water in regions where clean water is not available. Researchers at the Institut Laue–Langevin ( ILL ) and the European Synchrotron Radiation Facility ( ESRF ) have used neutrons and X-rays, respectively, to identify and characterize key proteins underlying the unique water purification properties of Moringa seeds. This information may allow better use of this abundant resource for sustainable water purification.

Paola Semeghini graduated with a degree in pharmaceutical chemistry from Modena University and worked for several years in the pharmaceutical industry. Since 2011, Paola has been a chemistry and scientific laboratory teacher at IIS Pascal, an applied science upper secondary school in Reggio Emilia, Italy, focusing on competence-based education and experiential learning.

Daniela Bergamotti manages the educational activities and projects promoted by Iren, a multiutility company operating in the waste, water, and energy sectors, in the Italian region of Liguria. Eduiren, the company’s educational division, is committed to building relationships with schools and communities, using a creative and inclusive approach to spread a culture of sustainability and achieve concrete changes.

Full link for United Nations statement: https://www.unep.org/interactives/beat-plastic-pollution/?gclid=EAIaIQobChMIm7eEuP6SgAMViX5MCh1XWQNZEAAYBCAAEgKFR_D_BwE 

The United Nations Environment Programme (www.unep.org) highlights the severe environmental, social, economic and health consequences of our addiction to single-use plastic products. Hence, this article, encouraging teachers to get their students to think about the pros and cons of using bottled water versus tap water is very timely. The article is also very balanced with opportunities to consider when bottled water may be essential.

Within the article there are different activities that teachers could adapt for different classes, including using internet research and the generously provided material provided with the article to understand the processes used to deliver clean tap water, an organised debate, a titration to determine water hardness and organising a blind water tasting test. Some of the ideas could also be used with a science club or to provide inspiration for individual or team science projects.

This article has many curriculum and cross-curricular links.

Curriculum topics include: critical analysis of data; fair testing; practical analysis skills; practical titration skills; practical titration skills; pH and pH indicators, acids and bases; metal ions; chemistry of limestone;

Cross-curricular links include:

Geography – availability of clean drinking water in different countries; the geography of rivers and the ‘rivalry’ for river water.

Earth Sciences – limestone sedimentary rocks;

Biology – biological uses of water; osmosis, water as a solvent e.g. for mineral ions

Suggested discussion questions:

• Is bottled water better than tap water?
• Why is ‘clean freshwater essential to human health and well-being’?
• What is the difference between ‘ground water’ and ‘surface water’?
• Why is bottled water seen by many as preferable to tap water?
• What are the main steps in water treatment before water arrives at your tap?
• What are the important considerations in carrying out a blind tasting of different waters?

Sue Howarth, UK

Supporting materials

Drinking water infosheet

Presentation evaluation rubric (PDF)

Presentation evaluation rubric (doc)

Local water task sheet

Debate evaluation rubric (PDF)

Debate evaluation rubric (doc)

Debate task sheet

Water hardness scale

Blind tasting questionnaire

Download this article as a PDF

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What do you want to find out about your study site’s water quality, how will I measure it and what are your predictions?

Check Your Thinking: Scenario: There is an abandoned mine dump within 5 meters of your study site stream. How might contaminants in the mine waste be impacting your stream? When would be the best time of year/day to collect water monitoring data that could help answer this question? What tests should you conduct?

Using your recorded observations and information compiled in the first step, the next step is to come up with a testable question. You can use the previously mentioned question (Based on what I know about the pH, DO, temperature and turbidity of my site, is the water of a good enough quality to support aquatic life?) as it relates to the limitations of the World Water Monitoring Day kit, or come up with one of your own.

What results do you predict? For example, your hypothesis may be “I believe the pH, DO, temperature and turbidity of the water at my study site are of good enough quality to support aquatic life because there are no visible impacts to water quality upstream or on the site.” Once you’ve formulated your question, begin planning the experiment or, in this case, the water monitoring you will conduct .

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The MSP project is funded by an ESEA, Title II Part B Mathematics and Science Partnership Grant through the Montana Office of Public Instruction. MSP was developed by the Clark Fork Watershed Education Program and faculty from Montana Tech of The University of Montana and Montana State University , with support from other Montana University System Faculty.

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• Why We’re Unique

Water Filtration

Introduction: (initial observation).

Humans may live for a month or more without food, but only a few days without water; only oxygen is more important. Each day, the body loses up to three quarts of water. A loss of only 10-20% of the body’s water content could be fatal.

When we take untreated water from a river or reservoir, the water often contains natural wastes and pollutants, such as bacteria, solids ( like mud, sand, and debris), inorganic minerals, and decayed organic compounds, as well as trace amounts of certain other contaminants. Such water is not good for human consumption.

Water suppliers transfer this water to a treatment plant where water will be filtered and chemically treated to be ready for human use.

People who have a water well at home, do a similar process in smaller scale and filter their own water.

There are also companies who offer varieties of filtration systems for home.

This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “ Ask Question ” button on the top of this page to send me a message.

If you are new in doing science project, click on “ How to Start ” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.  

Project advisor

Information Gathering:

There are many government organizations who research, control and offer information about water and water treatment. Food and drug administration (FDA) and Department of environmental protection (DEP) are among the best sources for information. Also many universities continuously research and offer courses about water filtration and treatment.

Following links are recommended for additional information.

• US Environmental Protection Agency (Office of Water)
• History of drinking water treatment (PDF)
• Water testing Scams
• Encyclopedia of Water Terms
• Home water treatment options
• Available Filtration Technologies

What are the impurities in water?

Water impurities are:

• Solids (Like mud, sand, debris, pollen, mold, fungal spores, dust mites, algae, cockroach dust, ..).
• Inorganic Minerals dissolved in water such as Calcium and Magnesium Salts.
• Decayed organic compounds from dead plants and animals and animal waste. These are the impurities that give a bad taste and odor to the water.

What are the sources of impurities?

• Wildlife that inhabits the water and the surrounding lands are a main cause of water contamination. Small animals such as fish, frog and insects excrete waste material from their bodies to the water.
• Mines and exposed acid producing minerals.

How each impurity is removed?

• Paper or fabric filters separate solid impurities such as mud, sand and dust.
• Ceramic or sand filters separate much of organic impurities from plants and animals. In municipal water treatment plants this separation is done by settling the organic material using Alum or Aluminum Sulfate.
• Carbon block filter removes oils, benzene, herbicides, pesticides and other volatile organic hydrocarbons.
• Granular activated carbon removes chemicals that cause bad taste and odors.

What is water treatment?

Water treatment is disinfection of water by killing disease causing virus, bacteria and parasites.

Water treatment is done by adding chlorine, ozone or using Ultra Violet light.

• Chlorine gas kills bacteria with adequate contact time.
• Ozone units super-oxygenate water which kills bacteria with adequate contact time.
• Ultraviolet light systems make use of the ability of this portion of the light spectrum to kill bacteria. Such systems are only effective on bacteria, viruses and some algae.

Using sand, ceramics and charcoal to filter water is a slow process and is not economical for large amount of water, that is why all water suppliers are using methods other than filtration.

What do water treatment facilities do?

Water treatment facilities purify large amount of water in large tanks using the following three steps.

First material floated on the water will be separated (Using steel mesh) Then other impurities will be settled slowly and by adding chemicals Finally Chlorine will be added for disinfection.

Question/ Purpose:

The purpose of this project is to learn about filtration, what it does and how it works. This project will also help us to know the difference between filtration and treatment.

Some of the specific questions that can be studies for this project are:

• How does the height of charcoal layer in a filter affect the rate in which organic impurities will be absorbed?
• How does the size of charcoal pieces in a filter affect the rate in which organic impurities will be absorbed?

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

If you are doing this project as a display project, you can skip this section. However, if you are doing this as an experimental project, then you will need to come up with questions, write your hypothesis, identify variables and do experiments to test your hypothesis.

For the above two questions that we have proposed, this is how you define variables.

• The height of charcoal layer is an independent variable (manipulated variable). The rate in which organic substances are absorbed is the dependent variable. Controlled variables are: Size of filter, concentration and type of pollutants, order and amount of filter material.
• The size of charcoal pieces is an independent variable (manipulated variable). The rate in which organic substances are absorbed is the dependent variable. Controlled variables are: Size of filter, concentration and type of pollutants, order and amount of filter material.

Hypothesis:

Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis. Following are two sample hypothesis for two questions suggested above.

• By increase in the height of charcoal layer, the rate of filtration of organic material will increase.
• Smaller size charcoal can result a higher rate of filtration. Large piece of charcoals may have no filtering affects at all.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1: Experiment with filters

Material Needed:

• 2-liter soda bottle, cut and dispose 2 inches from the bottom (by an adult)
• napkins or paper towels
• gravel, sand and cotton balls for your filter
• Charcoal (Cheapest one that don’t have liquid fuel added and have no odors)
• dirty water, (If you cant find any, make it yourself)  Instructions:
• Put the the soda bottle upside-down (like a funnel) and secure it so it will remain that way. You may do it by making a stand for that or hang it from some place.
• Layer the filter materials inside the soda bottle. Think about what each material might remove from the dirty water and in what order you should layer the materials. For an added challenge, use one additional materials to build your filter.
• Pour the dirty water through the filter. What does the filtered water look like?
• Take the filter apart and look at the different layers. Can you tell what each material removed from the water?
• Wipe the bottle clean and try again. Try putting materials in different layers or using different amounts of materials.

Exact measurements of the layers are optional; however, they affect the quality and the price of your filter. For example you may use a lot of activated carbon in your filter. In this case your filter will be very good, but it will also become expensive. On the other hand if you use a lot of sand with no or little activated carbon, then your filter will not be good and it will be cheap.

Now it’s time to experiment. Think of a question you want answered. Like, are there better materials for cleaning water? Be sure to predict what you think is going to happen. Then, test it out using different materials and record the results for your report.

Other samples:

• Water Filter
• Water Plant tour

Following are sample images of water filtration experiment. Material used for filtration in these images are Fish tank charcoal, Sand, Gravel and Coffee Filter

Experiment 2:

Test the effect of charcoal layer on filtration of organic compounds.

• Mix some food coloring with water to simulate water polluted with organic material.
• Make 3 identical filters with different heights of charcoal layer.
• Filter two cups of the colored water that you have made with each of your three filters.
• Compare the color of three filtered waters and record the results. Visually determine the rate of filtration (or the rate of color loss) and write that in your results table.

Your results table may look like this:

Height of charcoal layer Rate of filtration

You may also use the above results table to draw a bar graph. 

Experiment 3: (Permittivity)

Compare the filtration time of different filter materials

Introduction:

In a multi-layer water filter, it takes certain amount of time for water to travel each layer. The total filtration time is the sum of the individual travel times for different layers. Travel time of water in each layer depends on how pores the materials are and the attraction forces between the molecules of water and the molecules of filter materials. In this experiment we compare some of the filtration materials for their speed of filtration also known as permittivity.

• Get 5 identical bottles. Fill each bottle with 100ml water and mark the water level.
• Get 5 identical funnels and place them on the bottles. Write the name of filter materials on the funnels or bottles.
• At the bottom of each funnel place a piece of plastic mesh or steel mesh (like those used in making sieves). This is used to hold the filter materials in place.
• Fill each funnel to half with different filtration materials. (Filtration materials may include sand, clay, activated carbon, or any other substance that may be used in filtration).
• To each funnel add some water to saturate the filtration materials. Wait about 5 minutes. Empty any water that are entered in bottles.
• Add 200ml water to each funnel.
• Record the time it takes for the first 100ml of water that leave the funnel and enter the bottle. Your data table may look like this:

Materials and Equipment:

Multi-layer filters are normally a cylindrical container with layers of filter material. Top layers usually separate large solids and debris from the water. Middle layers separate much finer impurities to create a clear water. Lower levels are usually activated carbon to separate hydrocarbons, gasoline, insecticides and impurities that cause bad taste and bad odor.

A typical filter may start with a layer of gravel at the bottom, and then large sand, fine sand, clay, activated carbon, fine sand again, and large sand on the top.

These filters can not separate all viruses, bacteria and other micro organisms. Micro organisms later must be destroyed using chlorine or other disinfectant material.

Since filter absorbs some micro organisms such as bacteria and viruses, these micro organisms will reproduce inside the filter and exit the filter in later uses. That’s why filter material must be renewed so often.

Some filters are made only from different types of sand.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.

Calculations:

If you do any calculations for your project, make sure to write your calculations in this section of your report.

Summery of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.

Conclusion:

Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.

References:

List of Related links. http://poolplaza.com/pool-filters.shtml

http://phys4.harvard.edu/~wilson/Feroze_Ahmed/Sec_3.htm

http://www.cc.cc.ca.us/pfp/Pfpfilter.htm

http://www.orival.com/water.shtml

Related information

How does a water softener work.

We call water “hard” if it contains a lot of calcium or magnesium impurities dissolved in it. Hard water causes two problems: It can cause “scale” to form on the inside of pipes, water heaters, tea kettles and so on. The calcium and magnesium precipitate out of the water and stick to things. The scale doesn’t conduct heat well and it also reduces the flow through pipes. Eventually pipes can become completely clogged. It reacts with soap to form a sticky scum, and also reduces the soap’s ability to lather. Since most of us like to wash with soap, hard water makes bath-time or shower-time less enjoyable. The solution to hard water is either to filter the water by distillation or reverse osmosis to remove the calcium and magnesium, or to use a water softener. Filtration would be extremely expensive to use for all the water in a house, so a water softener is usually a less costly solution. The idea behind a water softener is simple. The calcium and magnesium ions in the water are replaced with sodium ions. Since sodium does not precipitate out in pipes or react badly with soap, both of the problems of hard water are eliminated. To do the ion replacement, the water in the house runs through a bed of small plastic beads or a chemical matrix called zeolite. The beads or zeolite are covered with sodium ions. As the water flows past the sodium ions, they swap places with the calcium and magnesium ions. Eventually the beads or zeolite contain nothing but calcium and magnesium and no sodium, and at this point they stop softening the water. It is now time to regenerate the beads or zeolite.Regeneration involves soaking the beads or zeolite in a stream of sodium ions. Salt is Sodium Chloride, so the water softener mixes up a very strong brine solution and flushes it through the zeolite or beads (this is why you load up a water softener with salt). The strong brine displaces all of the calcium and magnesium that has built up in the zeolite and replaces it again with sodium. The remaining brine plus all of the calcium and magnesium is flushed out through a drain pipe. Regeneration can create a lot of salty water.

What is “activated charcoal” and why is it used in filters?

Charcoal is carbon. Activated charcoal is charcoal that has millions of tiny pores between the carbon atoms. According to Encyclopedia Britannica, “The use of special manufacturing techniques results in highly porous charcoals that have surface areas of 300-2,000 square meters per gram. These so-called active, or activated, charcoals are widely used to adsorb odorous or colored substances from gases or liquids.” The word adsorb is important here. When a material adsorbs something, it means that it attaches to it by chemical attraction. The huge surface area of activated charcoal gives it countless bonding sites. When certain chemicals pass next to the carbon surface they attach to the surface and are trapped.

Activated charcoal is good at trapping other carbon-based impurities (“organic” chemicals), as well as things like chlorine. Many other chemicals are not attracted to carbon at all – sodium, nitrates, etc. – so they pass right through. This means that an activated charcoal filter will remove certain impurities while ignoring others. It also means that, once all of the bonding sites are filled, an activated charcoal filter stops working. At that point you must replace the filter.

Water Filters General Information Activated charcoal (activated carbon) filters have been used in homes to remove taste and odor. Taste and odor, although undesirable, are generally not considered unhealthy. In recent years, however, activated charcoal filters have been used to remove some of the contaminants that have been discovered in water supplies.

Activated charcoal is most effective at removing organic compounds such as volatile organic compounds, pesticides and benzene. It can also remove some metals, chlorine and radon. As with any treatment system, it cannot remove all possible drinking water contaminants.

Because activated charcoal systems are limited in the types of compounds they can effectively remove, it is essential that the homeowner determine which water contaminants are present before purchasing such a system. Anyone who suspects they have a water quality problem should first have their water analyzed by their local health department or a reputable laboratory. These analyses are costly, but worth the expense since they are necessary to determine the appropriate home treatment system and how best to operate such a system. A state or local health official can interpret water analysis results. Some laboratories may also provide this service.

Note that home water treatment is considered only a temporary solution. The best solutions to a contaminated drinking water problem are to either end the practices causing the contamination or change water sources. Activated charcoal is a black solid substance resembling granular or powdered charcoal. It is extremely porous with a very large surface area. Certain contaminants accumulate on the surface of the activated charcoal in a process called adsorption. The two main reasons that chemicals adsorb onto activated charcoal are a “dislike” of the water, and attraction to the activated charcoal. Many organic compounds, such as chlorinated and non- chlorinated solvents, gasoline, pesticides and tri-halo-methane can be adsorbed by activated charcoal. Activated charcoal is effective in removing chlorine and moderately effective in removing some heavy metals. Activated charcoal will also remove metals that are bound to organic molecules. It is important to note that charcoal is not necessarily the same as activated charcoal. Activated charcoal removes vastly more contaminants from water than does ordinary charcoal.

Home activated charcoal treatment systems are quite simple. The activated charcoal is normally packaged in filter cartridges that are inserted into the purification device. Water needing treatment passes through the cartridge, contacting the activated charcoal on its way to the faucet. Activated charcoal filters eventually become fouled with contaminants and lose their ability to adsorb pollutants. At this time, they need to be replaced. Activated charcoal treatment systems are typically point of use installed where they typically treat water used for drinking and cooking only. Activated charcoal filters can be placed on the end of the faucet, on the countertop, or under the sink. Point of use systems often have a bypass so that water for purposes other than drinking and cooking can also be dispensed at the tap without being treated. This increases the life of the activated charcoal, reducing the time between filter replacements.

A point of entry system is more appropriate if a contaminant is present that poses a health threat from general use as well as from consumption. Volatile organic compounds and radon are examples of this type of contaminant. These contaminants may get into the indoor air when water is used for showering and washing. In this case, it is more economical to have a large pint of entry system that treats water as it enters the home than to have point of use systems at each tap.

Activated charcoal filters used for home water treatment contain either granular activated charcoal or powdered block charcoal. The amount of activated charcoal in a filter is one of the most important characteristics affecting the amount and rate of pollutant removal. More charcoal in a cartridge means more capacity for chemical removal, resulting in longer cartridge lifetime. This means fewer cartridge changes and less chance of drinking contaminated water. Particle size will also affect the rate of removal; smaller activated charcoal particles generally show higher adsorption rates. Rust, scale, sand or other sediments can clog any activated charcoal filter. A solution to this problem is to place foam or cotton filters (often called sediment or fiber filters) between the cartridge and incoming water. When sediment filters become clogged, they need to be replaced or they will cause water pressure to drop.

An activated charcoal filter must be deep enough so that the pollutants will adsorb to the activated charcoal in the time it takes the water to move through the filter. The appropriate filter depth depends on the flow rate of water through the filter. The slower the flow rate, the better the removal. The poor performance of some end of faucet devices is probably due to improper filter depth.

Physical and chemical characteristics of the water will also affect performance. The acidity and temperature can be important. Greater acidity and lower water temperatures tend to improve the performance of activated charcoal filters. Activated charcoal filters have a limited lifetime. Eventually, the surface of the activated charcoal will be saturated with adsorbed pollutants and no further purification will occur. This is called breakthrough; the pollutants have broken through the filter to emerge in the treated water. When this occurs, it is possible that the contaminant concentrations in the treated water will be even higher than those in the untreated water. At this time, the cartridge needs to be replaced. Knowing when breakthrough will occur and thus when to replace the cartridge is a major problem with activated charcoal treatment.

Some cartridges are sold with predictions about their longevity. These are generally only crude estimates since they do not take into consideration factors that are characteristic to a specific water source, such as pollutant concentration. The retailer you purchase the treatment device from can make better estimates of the filter’s useful lifetime based on water usage (flow rate) and pollutant concentrations shown in the chemical analysis. Hence, to get the most accurate estimates, you should learn what these amounts are before purchasing the system. Note that if pollutant concentrations increase over time and testing is not performed to reveal this change, such estimates may turn out to be not very practical or useful.

Unfortunately, activated charcoal filters can be excellent places for bacteria to grow. Conditions for bacterial growth are best when the filter is saturated with organic contaminants, which supply the food source for the bacteria, and when the filter has not been used for a long period of time. It is still unclear whether the bacteria growing on the charcoal poses a health threat. Some manufacturers have placed silver in the activated charcoal in order to prevent the growth of bacteria. The effectiveness of this procedure has not been independently verified. In addition, silver may contaminate the drinking water.

The above considerations have led public health officials to consider activated charcoal home treatment a temporary solution to be used only until the source of contamination can be eliminated and the water supply is safe. Even with proper installation, maintenance and operation, malfunction of home water treatment systems can occur.

Activated Charcoal Filter Guidelines

Make sure the filter contains activated charcoal. Know the quantity of activated charcoal in the filter since this will determine the amount and rate of pollutant removal. Use pre-filter to add life to activated charcoal filters. Replace pre-filters and activated charcoal filters regularly. Determine appropriate intervals for replacement of activated charcoal filters based on contaminant concentration, water characteristics, water flow rate, depth of filter, type and amount of activated charcoal and prefilter. Retailers can help in this analysis.

It is always important for students, parents and teachers to know a good source for science related equipment and supplies they need for their science activities. Please note that many online stores for science supplies are managed by MiniScience.

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Drinking Water Will Not Keep You From Aging

“Drinking eight glasses of water every day can prolong your life for up to 15 YEARS and slash the risk of heart attacks, strokes and dementia, study suggests” Can that be true? The study was all over the media, but even a cursory read shows that drinking water was never measured, and eight glasses a day was never discussed.

The study, which so captured media attention, begins with a call to continue the work of Ponce de Leon in finding the Fountain of Youth.

“A new research field of geroscience [sic] aims to develop safe, practical, and widely available interventions targeting aging: a common driver of chronic diseases.”

So, it is fitting that in this modern day search for the Fountain of Youth the researcher sought optimal hydration.

The Current Study

The current work is part of a long series of studies by the author mining data from the Atherosclerosis Risk in Communities (ARIC) database – an ongoing, longitudinal survey of individuals from 4 US communities. Participants have been seen five times over roughly 30 years. The goal of this study was “to find out whether higher serum sodium at middle age is associated with accelerated aging and to identify serum sodium thresholds that can be used in clinical practice to identify people at risk who can potentially benefit from improved hydration.”

"We used serum sodium, that increases when we drink less fluids, as a proxy for the hydration habits of study participants."

The degree of hydration has never been measured in the ARIC participants; we have no idea how much water they did or did not drink. There are good reasons to use serum sodium as its proxy – sodium exerts the most significant force of the circulatory elements on our water volume. It is critical in triggering thirst and other mechanisms we use to increase or decrease our water intake. Elevated blood glucose can also alter that response, but individuals with diabetes were excluded from entry into the study.

There are also reasons that sodium may be a poor measure of hydration. Our physiology maintains serum sodium within a range that is “stable within 2–3 mmol/l interval between visits 1 and 2, 3 years apart,” but we have no data to correlate a specific degree of hydration with a point along the serum sodium range. In a different study looking at hydration in participants in the NHANES longitudinal study, total water consumption among participants, from water, beverages, and the water within food, varied from 1687 ml to 4981. They, too, found that underhydration was associated with increased mortality but that the chosen beverage made a difference, in some instances decreasing the risk of cancer while simultaneously increasing the risk of heart disease.

Two of the variables that were followed also come with uncertainty. The endpoints were age-related chronic disease and all-cause mortality. But ARIC looks only at cardiovascular risk and disease, arguably the problems most impacted by our circulatory system; the effect of serum sodium on cancer is unanswered. The other factor they considered was biological age, a mathematical construct based on 9 to 15 biomarkers [2]

The researchers presented no specific hydration guidelines. Here is what they wrote:

“Although the general importance of adequate hydration is generally recognized …long-term clinical studies, are lacking. … It is also recognized that establishing recommendations for water requirements that meet the needs of all persons is impossible because individual fluid needs differ because of variations of factors that influence water loss and solute balance, such as activity, nutrition, environment, and disease.”

- Natalia I. Dmitrieva, corresponding author

The study is fascinating. Unfortunately, most of us will go away with the idea that if we just drink more fluids, we will live longer, something the researchers never prove or suggest. But before throwing out the baby with the bathwater, consider this early statement from the study’s introduction:

"In the current study, we test the hypothesis that optimal hydration may slow down the aging process. … This hypothesis was inspired by previous mouse studies in which lifelong water restriction, increasing serum sodium by 5 mmol/l, shortened the mouse lifespan by 6 months which corresponds to about 15 years of human life.”

In some ways, their intention is far more revealing than this current data mining. Let’s look at their motivation, beginning with a caveat. The normal range of serum sodium for mice differs from humans and within breeds. But the rise in serum sodium associated with water deprivation would correlate well with the high sodium levels in the ARIC study

Mice were chronically deprived of water by providing a meal consisting of 30% water and 70% dry food without any other water source. Biochemical markers indicated that despite sodium values within normal ranges, their physiological mechanism compensated for a “chronic state of mild dehydration.” There were no apparent changes between these water-restricted (WR) mice and the controls that received the same amount of food but had no restrictions on their water intake over the first year. In the second year, the WR mice suddenly lost weight and experienced a shortening of their life by approximately 18% compared to controls.

There were other changes for those WR mice:

• Body composition changed in year two as they lost body fat and weight
• They ate more food throughout the study than controls. This may be partly trying to relieve their thirst; after all, that was the only water source. But normally hydrated mice reduce their eating when faced with diminished available water.
• Metabolically they resembled their cousins, the “desert hopping mouse Notomys alexis ,” a creature adapted to an environment with little water. The desert mice and the water-restricted mice both increased their food consumption. The reason; they could metabolically unlock water from their food. “WR mice remodeled metabolism toward metabolic water formation that allowed them to respond efficiently to a water deficit and stay in water balance. … to achieve such efficiency the WR mice had to increase energy expenditure … This reaction is a risk factor for accelerated aging ….and could contribute to a decreased life span” [2]. This increased energy expenditure also explains the fat loss in their later year, as it was utilized for calories.

• The WR mice did have elevations of coagulation factors, indicating the presence of a low-grade thrombotic state.
• An inflammatory marker, IL-6, was normal during the first year of life, but during the second, as aging usually increases inflammation, both the WR and control mice saw increased levels. The WR levels were markedly higher, suggesting accelerated inflammation.

While it was not reported in the current study, ARIC participants demonstrated low-grade inflammation and a prothrombotic state, as was seen in the WR mice. Previous work had shown that sodium levels at the high end of the normal range were associated with hypertension and elevated cholesterol.

As a physician, I find this nuance to our physiology fascinating. The normal range of sodium is a statistical construct, and where those at the ends of the spectrum become “abnormal” is now a bit fuzzier from this research. The research “identified a clear threshold of 141.5 mmol/L for serum sodium concentration above which the risk of the development of chronic age-related diseases greatly increases.” But as to the media’s interpretation that we need only drink more fluids, the last word goes to the researchers from their inspirational mouse study:

“Existence of individualized osmotic “set-points” …could create challenges for serum sodium and osmolality decrease by simple modifications of water and salt intake for people whose higher sodium levels are the result of their higher osmotic “set-point” as opposed to habitual low water and high salt intakes.”

[1] Those factors included “cardiovascular (systolic blood pressure), renal (eGFR, cystatin-C, urea nitrogen, creatinine, uric acid), respiratory (FEV), metabolic (glucose, cholesterol, HbA1c, glycated albumin, fructosamine), immune/inflammatory (CRP, albumin, beta 2-microglobulin).”

[2] The basis for this last statement that energy expenditure is a risk factor for accelerated aging comes from a hypothesis called the Redox theory of aging. You can find a more extended exposition of that belief here .

Source: Middle-age high normal serum sodium as a risk factor for accelerated biological aging, chronic diseases, and premature mortality eBioMedicine DOI: 10.1016/j.ebiom.2022.104404

Suboptimal hydration remodels metabolism, promotes degenerative diseases, and shortens life Journal of Clinical Investigation Insight DOI: /doi.org/10.1172/jci. insight.130949.

View the discussion thread.

By Chuck Dinerstein, MD, MBA

Director of Medicine

Dr. Charles Dinerstein, M.D., MBA, FACS is Director of Medicine at the American Council on Science and Health. He has over 25 years of experience as a vascular surgeon.

Latest from Chuck Dinerstein, MD, MBA :

The impact of water consumption on hydration and cognition among schoolchildren: Methods and results from a crossover trial in rural Mali

Roles Formal analysis, Writing – original draft

Affiliation Department of Environmental Health, Emory University Rollins School of Public Health, Atlanta, Georgia, United States of America

Roles Data curation, Investigation, Methodology, Project administration, Supervision, Writing – review & editing

Roles Methodology, Resources, Writing – review & editing

Affiliation School of Psychology, University of East London, London, United Kingdom

Roles Project administration, Supervision, Writing – review & editing

Affiliation Monitoring, Evaluation, and Learning Section, Save the Children Mali, Bamako, Mali

Roles Conceptualization, Funding acquisition, Methodology, Supervision, Writing – review & editing

* E-mail: [email protected]

• Anna N. Chard, 
• Victoria Trinies, 
• Caroline J. Edmonds, 
• Assitan Sogore, 
• Matthew C. Freeman

• Published: January 17, 2019
• https://doi.org/10.1371/journal.pone.0210568
• Reader Comments

Adequate provision of safe water, basic sanitation, and hygiene (WASH) facilities and behavior change can reduce pupil absence and infectious disease. Increased drinking water quantity may also improve educational outcomes through the effect of hydration on attention, concentration, and short-term memory. A pilot study was conducted to adapt field measures of short-term cognitive performance and hydration, to evaluate levels of hydration, and to investigate the impact of providing supplementary drinking water on the cognitive performance of pupils attending water-scarce schools in rural Mali. Using a cross-over trial design, data were collected under normal school conditions (control condition) on one visit day; on the other, participants were given a bottle of water that was refilled throughout the day (water condition). Morning and afternoon hydration was assessed using specific gravity and urine color. Cognitive performance was evaluated using six paper-based tests. Three percent of pupils were dehydrated on the morning of each visit. The prevalence of dehydration increased in the afternoon, but was lower under the water condition. Although there was a trend indicating drinking water may improve cognitive test performance, as has been shown in studies in other settings, results were not statistically significant and were masked by a “practice effect.”

Citation: Chard AN, Trinies V, Edmonds CJ, Sogore A, Freeman MC (2019) The impact of water consumption on hydration and cognition among schoolchildren: Methods and results from a crossover trial in rural Mali. PLoS ONE 14(1): e0210568. https://doi.org/10.1371/journal.pone.0210568

Editor: Michael L. Goodman, University of Texas Medical Branch at Galveston, UNITED STATES

Received: January 24, 2018; Accepted: December 27, 2018; Published: January 17, 2019

Copyright: © 2019 Chard et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: All relevant data are within the paper and its Supporting Information files.

Funding: Funding was provided by the Emory University Research Committee ( http://www.urc.emory.edu/grants/urc/index.html ). MCF received funding (grant number N/A). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.

Introduction

Health and educational benefits associated with improved water, sanitation, and hygiene (WASH) in schools include reduced diarrhea, absence, acute respiratory infection, and soil-transmitted helminth infection [ 1 – 5 ]. The availability of water during the school day is essential for supporting personal hygiene, sanitation, and maintaining a clean school environment. Increased access to water for drinking at school may also directly affect pupils’ academic performance through the cognitive benefits associated with decreased dehydration [ 6 – 8 ].

A recent UNICEF report found that only 53% of schools in least developed and other low-income countries had access to adequate water facilities, highlighting a gap in access to year-round, reliable, and safe water supply in sufficient quantities to support students’ needs [ 9 ]. Two studies assessing dehydration prevalence among school-age children living in hot, arid regions found that approximately two-thirds of children were in a state of moderate to severe dehydration [ 10 , 11 ].

The impact of dehydration on cognitive performance is well studied among adults in experimental settings. Dehydration induced through exercise or heat stress has been associated with decreased short-term memory [ 6 , 8 ], long-term memory [ 8 , 12 ], arithmetic efficiency [ 6 ], visuospatial function [ 6 ], and attention [ 7 ]. Few studies have investigated the relationship between dehydration and cognition in children. Evidence from three intervention studies in the United Kingdom corroborate findings among adults, suggesting that drinking water was associated with better scores of attention [ 13 , 14 ], short-term memory [ 14 – 16 ], and visual search [ 13 ]. However, these studies did not collect biometric measures of hydration status. Two additional studies conducted among children in Israel and Italy that assessed hydration status through urine osmolality found that dehydration was associated with decreased short-term memory [ 10 , 16 ].

Linking drinking water availability directly to cognitive skills among children in water-scarce areas would have important public health and policy implications. A deeper understanding of the relationship between hydration and cognition could provide significant and novel evidence for the importance of improving water access in schools. Here, we aim to address the gaps in existing literature by assessing the relationship between water consumption, hydration, and cognition in a setting where children do not commonly have water access during the school day.

We assessed the prevalence of dehydration among children attending schools in Mali, West Africa, and examined the effect of drinking supplementary water during the school day on hydration status and on cognitive test scores. Our hypothesis was that the majority of students would be dehydrated and that the provision of supplementary water would be associated with improved hydration and improved cognition. Methods included the piloting and refining of cognition measurements that had not been previously used in sub-Saharan African field settings. In addition, to our knowledge we collected one of the first sets of data indicating biometric levels of dehydration and reporting on the cognitive effects of dehydration in sub-Saharan Africa or elsewhere in the global South, where access to water is the poorest.

Materials and methods

We conducted a pilot study to investigate the impact of providing supplementary drinking water on the cognitive performance of pupils in water-scarce schools in rural Mali. The purpose of this study was to 1) pilot measures of short-term cognitive performance, 2) pilot field measures of hydration, 3) pilot data collection procedures for potential inclusion in a larger trial, 4) evaluate levels of dehydration among primary school students in water-scarce settings, and 5) test the association between drinking water and hydration on various measures of cognitive performance.

Data collection took place between January 7–10 and March 4–7, 2013 at two rural primary schools within 20 km of Sikasso town, Mali. Data collection at the second school was delayed due to armed conflict within the country. The maximum high temperature for data collection was 29°C in January and 40°C in March.

School eligibility, school selection, and participant selection

Schools were eligible for inclusion if they had no water point access within 0.5 kilometers, were within 1.5 hours drive from Sikasso town, and had at least 60 students in grades three through six. Two schools meeting eligibility requirements were purposively selected based on logistical considerations.

A total of 120 pupils in grades five (ages 9–13) and six (ages 10–16) were recruited. At each school, 30 pupils from each grade were randomly selected from school rosters using random number lists. In the event a pupil was absent or did not wish to participate, we continued to select pupils randomly from the class rosters until a sample size of 30 was reached for each grade.

Study design

We employed a crossover trial design in which each pupil in the study served as his or her own control. A crossover design was selected over a randomized controlled trial design due to the logistical challenge of randomizing water distribution within classrooms. Given the novel study procedures, crowded school setting, and limited timeframe, we were not certain that we could ensure water was not shared between pupils in intervention and control groups.

Hydration and cognition measurements were collected on two different days at each school. On one of the visit days we collected data without changing any conditions at the school (the control condition). On the other visit day we provided all pupils, regardless of participation in the study, with a 1.5 litre bottle of water in the morning, encouraged them to drink throughout the day, and refilled their bottle upon request (the water condition). We did not track the amount of water each pupil consumed. To account for confounding due to becoming familiar with the test (henceforth referred to as “practice effect”), the order of intervention days was counterbalanced between schools so that one school received water on the first day, while the other received water on the second day. Additionally, we included a separation of three days between visits.

To evaluate potential confounders or effect modifiers of hydration and cognition, participants were asked if they had anything to eat or drink that morning and reported drinking water availability at school. Staff members also made observations of drinking water availability at the school on the day of the visit. The majority of pupils went home at noon and returned for afternoon classes. We did not record lunch practices.

Measures of hydration

We collected three measures of hydration: urine specific gravity (U sg ), urine color (U col ), and self-reported thirst. Both U sg and U col are inexpensive measurements that can be easily conducted in the field with minimal training. They are strongly correlated with urine osmolality [ 17 , 18 ], a common measure of hydration in non-laboratory settings [ 10 , 11 , 16 ]. U sg measures urine density compared with water and was measured with ATAGO MASTER-URC/NM urine specific gravity analog refractometers (model 2793, ATAGO U.S.A. Inc., Bellevue, WA) [ 18 ]. The refractometers were calibrated using distilled water and were recalibrated at least every 15 readings, according to manufacturer instructions. U col was measured against a validated scale of eight colors [ 17 , 18 ]. Two trained enumerators independently evaluated each sample, and re-evaluated the sample together if their independent values differed; a third trained enumerator was consulted if no consensus was reached. Self-reported thirst [ 13 , 19 ] was collected on a five-point pictorial scale based on the Wong-Baker FACES pain rating scale [ 20 ]. For analysis, the least-thirsty image was assigned a value of 5 and values decreased to 1 as reported thirst increased.

Pupils provided urine samples between 8 and 9 am and again between 2–3 pm on each day of data collection. All urine analyses were conducted on the school grounds by trained study enumerators. Pupils self-reported thirst in the afternoon, after the completion of cognitive testing.

Measures of cognition

Cognition was measured using six tasks that assessed visual attention, visual memory, short-term memory, and visuomotor skills. These tests were taken from previous research on hydration and cognition that was conducted with children in Israel and the United Kingdom [ 10 , 13 , 14 ], piloted in Mali, and adapted to the Malian context.

Letter cancellation.

This test assesses visual attention . Pupils were given a grid containing target letters randomly dispersed among non-target letters and were given one minute to cross out as many target letters as possible. Scores were calculated by subtracting the number of non-target letters identified from the number of target letters identified; the maximum test score was 38.

Direct image difference.

This test assesses visual attention . Two nearly identical pictures were presented side-by-side. Pupils were given one minute to circle differences between the two images. Scores were calculated by subtracting the number of incorrect differences identified from the number of correct differences identified; the maximum test score was 9.

Indirect image difference.

This test assesses visual memory . Two nearly identical pictures were presented in sequence. Pupils were given ten seconds to study the first image. They were then briefly presented with a blank page, followed by a second image, and given one minute to circle the differences between the two images on the second image, without returning to the first. Scores were calculated by subtracting the number of incorrect differences identified from the number of correct differences identified; the maximum test score was 9.

Forward digit recall.

This test assesses short-term memory . Twelve sequences of numbers two to seven digits in length were read aloud to pupils at a rate of one number per second. Pupils were asked to write down the sequence in order after the sequence was read aloud. Two scores were derived from this test: the total number of correctly recalled sequences (maximum score of 12) and the maximum digit span of the correctly recalled sequence (maximum score of 7).

Reverse digit recall.

This test assesses short-term memory . Ten sequences of numbers two to five digits in length were read aloud to pupils at a rate of one number per second. Pupils were asked to write down the sequence in reverse order after the sequence was read aloud. Two scores were derived from this test: the total number of correctly recalled sequences (maximum score of 10) and the maximum digit span of the correctly recalled sequences (maximum score of 5).

Line tracing task.

This test assesses visuomotor skills . Pupils were presented with two curved parallel lines. They were given fifteen seconds to draw a line between them as quickly as possible while attempting not to touch the printed lines. Scores were calculated by subtracting the number of times the pupil’s line touched the side from the total length of the line in centimeters; the maximum test score was 29.

All cognitive tests were paper-based and administered by trained study staff in a group setting within the school classrooms. Testing sessions were standardized using written scripts. Staff introduced each test with a scripted explanation and an example, with no breaks between tests. Testing sessions lasted a total of 60–75 minutes and began at 3:00 pm in the afternoon of each visit. Each pupil in the study completed the testing session twice, once on the control condition day and once on the supplementary water condition day. Four parallel versions of each test were developed so that individual pupils did not receive the same test twice and pupils sitting next to each other did not receive the same test. All four test versions were distributed at each testing session. Tests were independently graded by two different staff members using fixed criteria. Grading criteria also provided guidelines to indicate whether or not pupils understood the tasks according to instruction. Tests with conflicting scores were examined by the study coordinator, who decided the final score for the task.

Data analysis

Data were entered into MS Excel and analyzed using STATA 13 SE. We tested both the impact of treatment condition (whether student was provided water or not during the day) and hydration status on change in test score. U sg was used to test the impact of hydration on change in test score because it was the only of our three hydration measures based on biomarkers, and is the most accurate of those three measures of hydration status [ 21 ]. A higher U sg indicates increased dehydration. Pupils were classified as dehydrated if they had a U sg of 1.020 or higher, which is equal to the dehydration threshold of urine osmology>800 mOsmol kg-1 H 2 O that has been used in previous studies of dehydration among children [ 10 , 11 , 16 ]. A total of eight scores for the six cognitive tests were calculated according to grading criteria. Scores were coded such that higher test scores on all cognitive tests represented better performance.

Univariable analysis

As proof of concept of the effect of water provision on hydration, we evaluated univariable differences in morning and afternoon hydration, U sg , and U col by treatment group using McNemar’s test statistic (binary variables) and paired sample t-tests (continuous variables). To evaluate the correlation between U sg , U col , and self-reported thirst, as well as the correlation between each of the cognitive test scores, pairwise tests of correlations between cognitive test scores were conducted using the pwcorr command. Lastly, to measure the presence of a “practice effect,” paired sample t-tests were used to assess differences in cognitive test scores between school visits.

Multivariable analysis

We examined the association between the provision of supplementary drinking water (treatment) and cognitive test scores as well as the association between pupil hydration (regardless of treatment) and cognitive test scores. These associations were assessed using separate mixed-effects linear regression models, where each cognitive test was the outcome, while treatment condition or hydration status, respectively, was the predictor covariate. Models included a random intercept at the pupil level to account for pupils acting as their own control. Unstandardized Beta coefficients are presented.

All models adjusted for multiple comparisons using the Bonferroni correction; as such, associations were considered significant if they had a p -value <0.006, the alpha necessary to reach 95% significance with eight hypotheses. Models were assessed for interaction and confounding with the following variables chosen a priori : pupil sex, pupil grade, reported drinking in the morning, reported eating in the morning, reported thirst, and morning hydration.

Interaction was assessed by running models of each cognitive test outcome with each predictor variable, potential interaction covariate, and an interaction term for the predictor and covariate (e.g. treatment*sex). Some variables initially indicated interaction at p <0.05. However, after adjusting for multiple comparisons using the Bonferroni correction, the only effect modifier to retain significance was pupil sex, which modified the relationship between afternoon dehydration and forward number recall- maximum digit span test score. Stratified results from this model are presented. All other associations were then tested for confounding; covariates significantly associated with the predictor variable as well as the outcome variable in independently run fixed-effect models were considered to be confounding variables. At p = 0.006, grade confounded the association between treatment and direct image difference & indirect image difference test scores, so was included as a control variable in these models. All models controlled for the visit day in order to account for a “practice effect” on cognitive tests.

We compared models from all pupils to models that excluded scores from pupils who did not complete cognitive tests according to instruction. There were no significant differences between model results, thus, we present the former results in order to maximize sample size. Only students with complete data for all measures of interest were included in analysis. We dropped 13 pupils due to absence on the second day of data collection, not being able to provide a urine sample, or inability to match pupils test scores and hydration measures due to improper identification procedures.

This study was approved by Emory University’s Institutional Review Board (IRB00062354), the Mali Ministry of Education, and the National Technical and Scientific Research Center ( Centre National de la Recherche Scientifique et Technique ) in Mali (001/2013-MESRS/CNRST). All three institutions approved consent in loco parentis (in the place of parents) due to the logistical challenges of finding and contacting parents in their homes, risk of lost wages to parents if they were summoned to school, and low levels of literacy making letters unfeasible. Permission for study activities and approval of a waiver of parental consent was also obtained from the Centres d’Animation Pédagogique (Center for Pedagogical Activity) and Académie d’Enseignement (Academy of Education) in Sikasso, both local government representatives responsible for education in the area where the study was conducted. Prior to commencing study activities at each school, we obtained consent in loco parentis from the school director and the Comité de Gestion Scolaire (school management committee), the organization empowered to oversee management and activities at the school, on behalf of the community that school serves. Pupils who were selected for the study provided informed verbal assent in a private setting prior to the start of data collection activities.

Study population

Data were collected from 120 pupils in two schools; of these, 107 (89.2%) pupils had complete data and were included in analysis. The sample was initially comparable in terms of sex, grade, and school. After removing pupils with incomplete data (n = 13), the final sample included 46 (43.0%) girls, 61 boys (57.0%); 58 (54.2%) pupils from grade five, 49 (45.8%) pupils from grade six; 47 (43.9%) from School 1, and 60 (56.1%) from School 2. The mean (sd) age was 11.6 (1.0) years in School 1 and 12.1 (1.7) years in School 2.

Univariable estimates of association with hydration

Only 3% of pupils were classified as dehydrated in the morning according to U sg (U sg >1.019), regardless of visit day or study condition. The difference between water and control condition mean morning U sg or U col was not statistically significant, and we found no difference in the prevalence of dehydration prior to distribution of water.

Pupils became more dehydrated throughout the school day under both study conditions. There was no significant difference in U col , self-reported thirst, or the prevalence of pupils classified as dehydrated in the afternoon under the water condition compared to the control condition. However, mean afternoon U sg was significantly higher under the control condition compared to the water condition ( Table 1 ). U sg and U col were strongly correlated both in the morning (r = 0.777, p <0.001) and afternoon (r = 0.734, p <0.001). Self-reported thirst, which was only measured in the afternoon, was not significantly correlated with either afternoon U sg (r = 0.089, p = 0.20) or afternoon U col (r = -0.003, p = 0.97).

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https://doi.org/10.1371/journal.pone.0210568.t001

Univariable estimates of association with cognition

Results from pairwise tests of correlations between cognitive test scores and results from the paired t-tests of the association between test score and visit day are shown in Table 2 . Most tasks were significantly correlated with at least one other task included in the battery of cognitive tests. Students achieved significantly higher scores on the second visit compared to the first visit for six of the eight cognitive tests, regardless of treatment condition.

https://doi.org/10.1371/journal.pone.0210568.t002

Multivariable estimates of association between cognitive test scores and treatment condition

In adjusted models, the provision of supplementary drinking water was significantly associated with two cognitive tests: reverse number recall (total) and line trace. Under the water condition, pupils performed better on the reverse number recall test. However, pupils had lower scores on the line trace test under the water condition ( Table 3 ).

https://doi.org/10.1371/journal.pone.0210568.t003

Multivariable estimates of association between cognitive tests scores and hydration status

We examined the impact of hydration on cognitive test performance, regardless of treatment condition. Neither hydration status, where a U sg greater than 1.019 indicated dehydration, nor U sg were significantly associated with any cognitive test score ( Table 3 ). The test for interaction indicated that pupil sex significantly modified the association between forward number recall (maximum) and afternoon dehydration. When stratified by sex, males performed worse when dehydrated (β = -0.14; 95% CI -0.54, 0.27; p = 0.501) and females performed better when dehydrated (β = 1.10; 95% CI 0.31, 1.89; p = 0.006); only the association between hydration and forward number recall among female pupils approached statistical significance.

We conducted a cross-over trial as part of a pilot study to examine the associations between water consumption, hydration, and cognition among pupils attending water-scarce schools. We successfully adapted measures of cognitive performance that could be completed by children in rural Malian schools and tested the feasibility of field hydration measures and data collection procedures within schools in Sub-Saharan Africa. Results demonstrated that supplementary water provision within a school setting significantly decreased U sg , even within a short time period. However, we found no effect of the impact of supplementary water provision on cognitive test scores.

This research refined a battery of cognitive tests for use with children in Mali which can be adapted to other developing settings. Research conducted in the U.K. concluded that their cognitive test of visual memory was too easy for the target population, indicated by many children achieving the maximum score on the test, and thus modifying study results [ 13 ]. Our results show that the percentage of children achieving the maximum score or the minimum score on any of the cognitive tests ranged from 0.5%-15.4% and 0.5–4.2%, respectively, indicating that the cognitive tests adapted for this trial were neither too difficult nor too hard. However, results from our pairwise tests of correlation indicate that the two tests measuring visual attention (letter cancellation and direct image difference) were not significantly correlated, suggesting that further adaptation may be needed on these tests to measure this target skill. Furthermore, while scores for each of the four tests measuring short-term memory were significantly associated with at least one other score in the suite of tests measuring that domain, they were very similar tests in that they all incorporated number recalls. Thus, correlation does not necessarily indicate that they were in fact measuring the cognitive skill they were intended to measure.

This is one of the first studies to employ existing field methodology to collect urine samples and measure dehydration among school children in low-resource school settings. Results from this pilot study were further refined in a subsequent trial in Zambia [ 22 ]. Prior research on dehydration among schoolchildren has relied predominantly on self-reported thirst as their measure for dehydration. Although evidence- particularly among healthy individuals- is limited, research has concluded that one’s thirst response is not an accurate measure of hydration [ 23 , 24 ]. We found no research investigating this association among children. Our results demonstrated no significant difference between self-reported thirst among pupils under the water condition compared to the control condition, even though the measurements of U sg indicated that pupils under the water condition had significantly higher levels of hydration than pupils under the control condition. Additionally, self-reported thirst and the biometric measurement of U sg were not significantly correlated. These findings support previous literature concluding that self-reported thirst is not an accurate measure of hydration. Given our findings, future research should consider utilizing only measurements that provide biometric evidence of dehydration. Data also revealed that U col , although strongly correlated with U sg , did not capture a significant difference in afternoon hydration between water and control conditions. We believe this may have been due to the subjective nature of matching urine color to the color chart. The use of refractometers to measure U sg required less training and took less time than measuring U col , and thus is recommended for future studies investigating dehydration levels of subjects in low-resource settings.

Our finding that only 2.8% of pupils were dehydrated in the morning stands in stark contrast to previous research which reported that 84% of Italian school children [ 16 ], 68% of Israeli school children [ 11 ], and 43% of Zambian schoolchildren [ 22 ] were dehydrated at the beginning of the school day. While this result was initially surprising, it may be partly explained by evolutionary mechanisms. In their research, Bar-David reported that among their sample of Israeli schoolchildren, Bedouin children, who originate from a population that has lived in the desert for many generations, had the lowest mean urine osmolality (the lowest prevalence of dehydration), possibly because their bodies adapted over time to have a lower threshold of thirst [ 10 , 11 ]. Thus, Malian children, who reside in hot, arid, and water-scarce environments, may have also adapted a greater resistance to dehydration, leading to a lower prevalence of dehydration at the beginning of the school day. Extremely low levels of morning dehydration may also be partly explained by the fact that a vast majority of students (93%) reported drinking something in the morning before going to school. We do not believe that pupils intentionally consumed more water than usual in preparation for participation in the research. Neither school officials nor pupils were aware of the study topic, activities, or pupil selection prior to the first day of the study. Thus, participants would not have had the foreknowledge to alter their normal drinking behaviors. Although school officials and pupils were aware of the date of the second visit, given that no significant differences in the prevalence of dehydration or U sg were observed between the first and second visits, it is unlikely that students changed their drinking practices for the second day.

Under both treatment conditions, dehydration increased throughout the day. Pupils had significantly lower U sg in the afternoon under the supplementary water condition than under the control condition, demonstrating the “proof of principle” that supplementary water provision improves hydration. However, there was no significant difference in the prevalence of afternoon dehydration among pupils in the water group compared to pupils in the control group. Nonetheless, when the significant impact of water consumption on increasing U sg is considered in light of findings of the relationship between drinking water and cognition from other contexts [ 13 – 16 ], there is evidence that providing drinking water at school may create a positive impact on pupil learning.

We found some evidence that supplementary water provision was associated with higher scores on cognitive tests, but few results were significant. These results are consistient with those from our follow-up trial among primary school children in Zambia [ 22 ]. Treatment was significantly associated with higher scores on the letter cancellation task, a result supported by previous literature that also found a positive relationship between provision of drinking water and performance on visual attention tasks [ 14 , 22 ]. While previous studies have reported no significant association between water provision and visuomotor skills [ 13 , 14 ], we found that scores on the line trace test were significantly, but negatively associated with supplementary water provision. Although this result was unexpected, it may be largely explained by a practice effect, in which pupils performed significantly better the second time they took the test, regardless of treatment condition. Although pupils took a different version of the test on each day, a practice effect was evident, as test scores significantly improved when pupils performed each task the second time. One possible reason for this difference could be that pupils in Mali are not accustomed to the types of activities performed during the tests, which were adapted from tests used in Western settings. Although the distribution of test scores and the correlation of tests measuring the same domain do indicate that the tests were suitably adapted to the context, the novelty of the tests may have caused a much lower baseline score at the first testing session. Pupils may need to practice completing the tasks several times in order to fully understand the tests before their scores are measured.

Lastly, evidence on the degree and duration of dehydration necessary to impact cognitive performance is limited. It is possible that the lack of significant improvements in cognitive performance following treatment is because one school day of supplementary water provision is not sufficient to reverse the impacts of chronic dehydration and impart cognitive benefits on schoolchildren; perhaps more long term water consumption is necessary for these benefits to be measurably improved [ 22 ]. Further, although the U sg data provide evidence that pupils drank under the treatment condition, we did not measure the volume of water consumed by subjects. Measuring the volume of water consumed by subjects and including a dose-response measure in the analysis could contribute to the discourse on how much water consumption is needed to improve hydration, and how much hydration is needed to improve cognition.

Limitations

There are several limitations to the current research. First and most crucial was the impact of the practice effect, in which pupils performed significantly better on cognitive testing during the second visit, regardless of treatment condition. Approaches to limit or account for the practice effect on cognitive testing in primary school populations residing in settings where this type of testing is uncommon requires additional attention; future research should focus on alternative trial designs to minimize this impact. Additionally, the fixed test order could have led to a learning effect across tests, where certain tests- conceivably later on in the series- revealed a more significant association due students becoming more comfortable with testing in general, rather than due to the skill tested. Students in both the intervention and control would have had the same learning effect, which would bias our results to the null, but there is no way to control for this within the individual models. However, we observed no trend where students performed differently on tests administered in the end of the suite on either testing day. Further, we reviewed the estimates of effect and do not find any effect modification. Second, because this was a pilot study, the sample was limited to 120 pupils in two schools. As such, the study may not have been sufficiently powered to detect significant but less strong impacts of supplementary water provision or hydration status on cognitive performance. Low levels of dehydration across study groups may have also further limited our ability to detect an impact. Third, we conducted an intention-to-treat analysis and did not measure or control for the volume of water consumed by the participants in the treatment group. We did not measure whether pupils in the control group consumed water brought from home, and we could not ethically restrict them from drinking water. We also did not record lunch practices among students, and cannot guarantee that children did not consume water when they went home for lunch. As such, we cannot unequivocally state that the intervention and control groups were separated by water consumption, or lack thereof. However, afternoon U sg was collected regardless of treatment condition, and results validate the degree of water consumption under treatment. Additionally, lunch practices among individual students would likely be similar across days, thus the influence of lunch practices would be consistent across test conditions since pupils act as their own controls. Fourth, due to external events, data collection at the second school was delayed for two months and occurred during a warmer period. The higher temperatures during the second data collection period may have impacted study results. Evidence suggests that exposure to heat may independently impact cognitive functions, however this research has not been conducted among children [ 25 – 27 ]. Although significantly more pupils in the second school were dehydrated in the afternoon compared to pupils in the first school, due to the crossover design, it is not possible to quantify the effect that temperature may have had on study outcomes. Last, the methodology, including the duration of tests, were adapted from cognitive tests previously used among primary school children [ 13 , 14 , 28 ], but the total testing time was longer than in previous studies due to the novelty of the tests in the population and our emphasis on explanation and examples. However, because there was no significant trend in scores across the testing suite, there is no evidence that performance worsened due to fatigue among students.

We suggest a two-step approach for collecting further evidence on hydration and cognition among pupils in water-scare schools. First, we recommend implementing a second trial with cognitive testing methodology that addresses the challenges of the practice effect in order to increase the evidence base on the link between hydration and cognition among schoolchildren in water scare areas. Once the link between improved hydration and cognition among schoolchildren has been established under experimental conditions, we recommend carrying out cross-sectional hydration testing in a larger sample of schools. Considering the apparent invalidity of self-reported thirst and the subjective nature of urine color evaluation, we recommend the use of urine specific gravity or another objective biometric measure for hydration testing. Given the evidence previously established, hydration in this case would serve as an easily quantified and measured proxy for pupil attention, memory, and concentration. Findings from this investigation could provide evidence of the benefit of drinking water access, and specifically on the construction of water points on school grounds, for pupils’ educational attainment.

Conclusions

This study represents novel research across multiple scientific disciplines and development sectors, and is an important step in developing clear and direct linkages between provision of WASH in schools and learning. Results demonstrated the proof of principle that increased water access improves hydration. Although we found no evidence for our hypothesis that improvements in hydration status leads to improvements in cognitive performance among pupils in water scare schools, results may have been masked by a strong practice effect, and the power to detect significant differences was limited. We demonstrated the feasibility of collecting biometric measurements of hydration status and testing cognitive abilities in resource-poor settings. Findings from this research and subsequent studies of hydration and cognition have broad significance for advocacy for international development and health sectors for increased attention to insufficient access to water supply for school children.

Supporting information

S1 file. data..

https://doi.org/10.1371/journal.pone.0210568.s001

Acknowledgments

This study was funded by the Emory University Research Committee. Additional in-kind support was given by Save the Children and Dubai Cares. We would like to thank Sarah Porter for assistance with development of the study, as well as Birama Diallo, Seriba Diallo, Makan Keita, Sadio Sangaré, and Mariam Traoré of Save the Children and Jérémie Toubkiss of UNICEF for their support.

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E.P.A. Says ‘Forever Chemicals’ Must Be Removed From Tap Water

The rule applies to a family of chemicals known as PFAS that are linked to serious health effects. Water utilities argue the cost is too great.

By Lisa Friedman

For the first time, the federal government is requiring municipal water systems to remove six synthetic chemicals linked to cancer and other health problems that are present in the tap water of hundreds of millions of Americans.

The extraordinary move from the Environmental Protection Agency mandates that water providers reduce perfluoroalkyl and polyfluoroalkyl substances, known collectively as PFAS, to near-zero levels. The compounds, found in everything from dental floss to firefighting foams to children’s toys, are called “forever chemicals” because they never fully degrade and can accumulate in the body and the environment.

The chemicals are so ubiquitous that they can be found in the blood of almost every person in the United States. A 2023 government study of private wells and public water systems detected PFAS chemicals in nearly half the tap water in the country .

Exposure to PFAS has been associated with metabolic disorders, decreased fertility in women, developmental delays in children and increased risk of some prostate, kidney and testicular cancers, according to the E.P.A .

Michael S. Regan, the E.P.A. administrator, called the new regulation “life changing.”

“This action will prevent thousands of deaths and reduce tens of thousands of serious illnesses,” Mr. Regan said on a call with reporters on Tuesday. He described the rule as the most significant action the federal government has ever taken to reduce PFAS exposure in drinking water.

“We are one huge step closer to finally shutting off the tap on forever chemicals once and for all,” he said.

The E.P.A. estimated it would cost water utilities about $1.5 billion annually to comply with the rule, though utilities maintain that the costs could be twice that amount and are worried about how to fund it. States and local governments have successfully sued some manufacturers of PFAS for contaminating drinking water supplies, but the settlements awarded to municipalities have been dwarfed by the costs of cleaning up the chemicals, municipal officials said.

Industry executives say taxpayers will ultimately foot the bill in the form of increased water rates.

The 2021 bipartisan infrastructure law provides $9 billion to help communities address PFAS contamination and the E.P.A. said $1 billion of that money would be set aside to help states with initial testing and treatment.

Mr. Regan announced the regulation on Wednesday in Fayetteville, N.C., near the site where, in 2017, a Chemours chemical plant discharged water contaminated with PFAS into the Cape Fear River, making the local drinking water unsafe.

Mr. Regan, who previously served as North Carolina’s top environmental regulator, oversaw the Cape Fear PFAS investigation at the time and forced Chemours to clean up the air, soil and water in the lower Cape Fear River basin communities.

In 2022, the E.P.A. found the chemicals could cause harm at levels “much lower than previously understood” and that almost no level of exposure was safe.

Under the new rule from the E.P.A., water utilities must monitor supplies for PFAS chemicals and would be required to notify the public and reduce contamination if levels exceeded the new standard of 4 parts per trillion for perfluoroalkyl and polyfluoroalkyl substances. Previously, the agency had advised that drinking water contain no more than 70 parts per trillion of the chemicals.

Public water systems have three years to complete their monitoring. If those samples show that levels of PFAS exceed the new E.P.A. standards, the utilities would have another two years to purchase and install equipment designed to filter out PFAS.

In a 2020 peer-reviewed study , scientists at the Environmental Working Group, a nonprofit organization, estimated that more than 200 million Americans had PFAS in their drinking water.

Public health advocates and scientists said the new regulation was overdue.

“A growing body of scientific research shows that PFAS chemicals are more harmful to human health than previously thought, and at extremely low levels,” said Anna Reade, director of PFAS advocacy at the Natural Resources Defense Council, an environmental group.

In just the past year, more than a dozen peer-reviewed studies have found evidence of additional health effects of PFAS exposure, including a delay in the onset of puberty in girls, leading to a higher incidence of breast cancer, renal disease, and thyroid disease; a decrease in bone density in teenagers, potentially leading to osteoporosis; and an increased risk of Type 2 diabetes in women.

Dr. Susan M. Pinney, the director of the Center for Environmental Genetics at the University of Cincinnati, led a longitudinal study of young girls who had been exposed to PFAS after an industrial plant in West Virginia released the chemicals into the Ohio River.

She called the number of people exposed to PFAS around the country “mind boggling.”

Robert A. Bilott, an attorney who has spent more than two decades litigating the hazardous dumping of PFAS chemicals, said he had alerted the E.P.A. to the dangers posed by the chemicals in drinking water as early as 2001. “It has taken far too long to get to this point, but the scientific facts and truth about the health threat posed by these man-made poisons have finally prevailed,” Mr. Bilott said.

The E.P.A. calculated the health benefits of the new regulation at about $1.5 billion annually from reductions in cancer, heart attacks and strokes and birth complications.

But Republicans and industry groups, along with many mayors and county executives, said the Biden administration had created an impossible standard that would cost municipal water agencies billions of dollars.

Several questioned E.P.A.’s accounting as well as the science used to develop the new standard.

The American Water Works Association, the Association of Metropolitan Water Agencies and other groups representing water utilities estimated that the cost of monitoring and remediation of PFAS could be as much as $3.2 billion annually. The figure is based on an analysis conducted for the American Water Works Association by Black & Veatch, a firm of consulting engineers.

Communities with limited resources will be hardest hit by the new rule, they said.

“When regulations are set near zero, that is not something manufacturers or water systems can economically achieve,” Brandon Farris, the vice president of energy policy at the National Association of Manufacturers, wrote in a letter to the E.P.A. “Regulations that are not economically achievable will lead to critical substances being manufactured outside of the U.S. where environmental protections are often less stringent.”

Christina Muryn, the mayor of Findlay, Ohio, a town of about 50,000 people, said that, while clean drinking water is an imperative, the E.P.A. was requiring municipalities to meet new mandates without adequate support.

“That is very frustrating to me as a citizen, as a mayor, and as someone who is responsible for our water treatment system,” Ms. Muryn said.

Public health advocates said the costs of the new rule were outweighed by the growing body of evidence of the dangers posed by PFAS.

Widely used since the 1940s, the chemicals are useful in repelling water and oil. Nonstick pans have been most famously associated with PFAS but the chemicals can be found in water-repellent clothes and carpets, certain shampoos, cosmetics and hundreds of other household items.

Lisa Friedman is a Times reporter who writes about how governments are addressing climate change and the effects of those policies on communities. More about Lisa Friedman

The Proliferation of ‘Forever Chemicals’

Pfas, or per- and polyfluoroalkyl substances, are hazardous compounds that pose a global threat to human health..

For the first time, the U.S. government is requiring municipal water systems to detect and remove PFAS from drinking water .

A global study found harmful levels of PFAS  in water samples taken far from any obvious source of contamination.

Virtually indestructible, PFAS are used in fast-food packaging and countless household items .

PFAS lurk in much of what we eat, drink and use, but scientists are only beginning to understand how they affect our health .

Though no one can avoid forever chemicals entirely, Wirecutter offers tips on how to limit your exposure .

Scientists have spent years searching for ways to destroy forever chemicals. In 2022, a team of chemists found a cheap, effective method to break them down .

EPA imposes first national limits on 'forever chemicals' in drinking water

For the first time, the Environmental Protection Agency has established national limits for six types of perfluoroalkyl and polyfluoroalkyl substances in drinking water.

The substances, known by the initialism PFAS, are nicknamed "forever chemicals" because they barely degrade and are nearly impossible to destroy , so they can linger permanently in air, water and soil.

As a class of chemicals, PFAS have been associated with a higher risk of certain cancers, heart disease, high cholesterol, thyroid disease , low birth weight and reproductive issues, including decreased fertility. 

Most people in the U.S. have PFAS in their blood , according to the Department of Health and Human Services.

The EPA announced Wednesday that levels of PFOA and PFOS — two types of PFAS commonly used in nonstick or stain-resistant products such as food packaging and firefighting foam — can’t exceed 4 parts per trillion in public drinking water. 

Three additional PFAS chemicals will be restricted to 10 parts per trillion. They are PFNA and PFHxS — older versions of PFAS — and GenX chemicals, a newer generation of chemicals created as a replacement for PFOA.

PFOA and PFOS are the most widely used and studied types of PFAS, according to the EPA. Companies started making them in the 1940s, but the substances were largely phased out of U.S. chemical and product manufacturing in the mid-2000s. However, they persist in the environment and have mostly been replaced by newer types of chemicals within the same class.

The EPA’s new limit reflects the lowest levels of PFOA and PFOS that laboratories can reasonably detect and public water systems can effectively treat. But, according to the agency, water systems should aim to eliminate the chemicals, because there is no safe level of exposure.

Eleven states already have regulatory standards for PFAS in drinking water. The EPA estimated that 6% to 10% of the country’s public water systems — 4,100 to 6,700 systems in total — will need to make changes to meet the new federal limits.

“One hundred million people will be healthier and safer because of this action,” EPA Administrator Michael Regan said Tuesday on a media call, referring to the number of people served by the water systems that will need upgrades.

As of Wednesday, public water systems that don’t monitor for PFAS have three years to start. If they detect PFAS at levels above the EPA limits, they will have two more years to purchase and install new technologies to reduce PFAS in their drinking water.

The EPA estimates that the new limits will prevent thousands of deaths and tens of thousands of serious illnesses.

One of the biggest health concerns associated with PFOA is an increased risk of kidney cancer . Exposure to high levels of PFOS has also been associated with an increased risk of liver cancer .

GenX chemicals have been shown in animal studies to damage the liver, kidneys and immune system, as well as liver and pancreatic tumors. According to studies in rodents, PFNA exposure could lead to developmental issues and PFHxS may disrupt the thyroid system. 

The EPA also set a limit Wednesday for mixtures of at least two of the following chemicals: PFNA, PFHxS, PFBS and GenX. Public water systems can use an equation provided by the EPA to determine whether the cumulative concentrations of the chemicals exceed the agency’s threshold. 

The EPA proposed limits to PFAS in drinking water last year. After it reviewed public comments, it made the limits official Wednesday.

“This is a huge, historic public health win,” said Scott Faber, senior vice president of government affairs for the Environmental Working Group, an activist group that advocates for stricter regulations of drinking water pollutants.

Faber called the new EPA limits “the most important step we’ve taken to improve the safety of our tap water in a generation” and “the single most important step we’ve taken to address PFAS ever.”

Jamie DeWitt, director of the Environmental Health Sciences Center at Oregon State University, said that although the new limits don’t end the problem of PFAS in drinking water, they represent significant progress.

“This is going to give people in contaminated communities at least a sense that the federal government cares about them and cares about their exposure, because I think many people living in PFAS-impacted communities have not felt heard,” she said. 

The EPA said Wednesday that $1 billion in funding is newly available to help states and territories implement PFAS testing and treatment at public water systems and to help owners of private wells do the same. The funding comes from the federal infrastructure law passed in 2021, which set aside $9 billion to address PFAS and other contaminants in water. The money will be distributed as grants.  

Some public water systems have also sued companies that manufacture or previously manufactured PFAS, aiming to hold them accountable for the costs of testing and filtering for PFAS. One such lawsuit resulted in a $1.18 billion settlement last year for 300 drinking water providers nationwide. Another lawsuit awarded $10.5 billion to $12.5 billion , depending on the level of contamination found, to public water systems across the country through 2036.

The most common way to remove PFAS from water is through an activated carbon filter, which traps the chemicals as water passes through. Other options include reverse osmosis or ion exchange resins, which act like tiny magnets that attract PFAS chemicals. 

But even once water is treated for PFAS, it can take a while to see positive impacts, said Anna Reade, director of PFAS advocacy at the National Resources Defense Council, a nonprofit environmental advocacy group. 

“For most of these six chemicals, it’s between two to eight years for the amount in our bodies to decrease by half. So we’re looking at years before we see some substantial decreases in our exposure over time,” she said.

The EPA’s new drinking water limits apply to only a small fraction of the more than 12,000 types of PFAS , so activists are still concerned about overall exposure.

“This is not the final step,” Reade said. “We still have a lot of other PFAS to worry about.”

Aria Bendix is the breaking health reporter for NBC News Digital.

Desalination: What is it and how can it help tackle water scarcity?

A natural resources crisis like water scarcity is listed in the World Economic Forum’s 2024 Global Risks Report, as one of the top-10 threats facing the world in the next decade. Image:  Unsplash/Nathan Dumlao

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Stay up to date:, food and water.

This article was originally published on 12 March 2024 and updated on 15 April 2024

• Desalination increases access to safe, clean drinking water, but the process is energy-intensive and costly.
• Innovations are harnessing wave power and other forms of energy capture to reduce reliance on fossil fuels and curb emissions from desalination.
• A natural resources crisis is one of the leading global long-term threats, according to the World Economic Forum’s 2024 Global Risks Report.

Billions of people turn on a tap and expect clean drinking water to flow out, but this is not the reality for billions of others.

Rapid population growth, urbanization and increased global water consumption by agriculture, industry and energy have left a growing number of countries facing the threat of water scarcity.

One solution to meet the growing demand for freshwater is desalination, which involves removing the salt from seawater to produce drinking water. While this process alone can’t prevent a global water crisis, it can play a vital role in providing more people around the world with access to clean, safe drinking water.

Have you read?

25 countries face extremely high water stress, study finds, this new desalination system is inspired by the ocean and powered by the sun, how technology and entrepreneurship can quench our parched world, a future water crisis.

Water scarcity occurs when water demand outstrips available supply during a specific period – when water infrastructure is inadequate or institutions fail to balance people’s needs.

In 2022, 2.2 billion people lacked safely managed drinking water , including more than 700 million people living without a basic water service, according to the United Nations.

By 2030, there could be a 40% global shortfall in freshwater resources, which combined with world population growth that’s set to increase from 8 billion today to 9.7 billion by 2050 , would leave the world facing an extreme water crisis.

Sub-Saharan Africa is expected to see the biggest change in water demand, with a projected 163% increase by mid-century, World Resources Institute data shows. This is four times the expected rate of change in Latin America, the second-highest region.

Almost two-thirds of the planet’s surface is covered with water, and our oceans hold 96.5% of all water on Earth . However, its salt content makes this water unsuitable for humans to drink. This is where desalination comes in.

Types of desalination

There are a number of different methods of desalination, but most work either by a process of reverse osmosis or multistage flash to remove the salt from seawater .

Reverse osmosis is the more efficient of these two methods. The process uses a special membrane acting as a filter, which blocks and removes salt from seawater as it passes through. Here, powerful pumps generate enough pressure to ensure pure water is extracted.

Multistage flash desalination doesn't use a filter. Instead, saltwater is exposed to steam heat and pressure variations, which causes a portion of the water to evaporate – or "flash" – into water vapour or freshwater, leaving behind salty brine as a by-product.

Water security – both sustainable supply and clean quality – is a critical aspect in ensuring healthy communities. Yet, our world’s water resources are being compromised.

Today, 80% of our wastewater flows untreated back into the environment, while 780 million people still do not have access to an improved water source. By 2030, we may face a 40% global gap between water supply and demand.

The World Economic Forum’s Water Possible Platform is supporting innovative ideas to address the global water challenge.

The Forum supports innovative multi-stakeholder partnerships including the 2030 Water Resources Group , which helps close the gap between global water demand and supply by 2030 and has since helped facilitate $1Billion of investments into water.

Other emerging partnerships include the 50L Home Coalition , which aims to solve the urban water crisis , tackling both water security and climate change; and the Mobilizing Hand Hygiene for All Initiative , formed in response to close the 40% gap of the global population not having access to handwashing services during COVID-19.

Want to join our mission to address the global water challenge? Read more in our impact story .

Both desalination processes create brine containing high salt levels, which can pose a threat to marine ecosystems when released back into natural bodies of water. The output of both methods is clean drinking water. But, in addition to removing salt, the desalination process also removes organic or biological chemical compounds so the water produced doesn’t transmit diarrhoea or other diseases.

Wave-powered innovation

While reverse osmosis plants are more efficient than multistage flash plants, large-scale desalination plants require a lot of energy and maintenance, and are expensive to build and operate.

A number of innovative desalination systems are being developed to try and reduce the energy required to operate them and related emissions.

Oneka, a wave-powered desalination technology, is one such innovation . Floating buoys tethered to the ocean floor use wave power to drive a pump that forces seawater through filters and reverse osmosis membranes. The fresh water is then piped ashore again powered solely by the natural motion of waves, explains Canadian desalination company Oneka Technologies.

The system has several advantages over large-scale shore-based desalination plants that are mostly powered by combusting fossil fuels, but it does require high waves to work.

The small floating units require 90% less coastal land compared with a typical desalination plant, for example, the company says. Relying on emissions-free wave power rather than electricity demands less energy and generates fewer emissions than traditional desalination plants.

" Desalination facilities are conventionally powered by fossil fuels ," Susan Hunt, Chief Innovation Officer at Oneka Technologies, told the BBC. "But the world has certainly reached a pivot point. We want to move away from fossil fuel-powered desalination."

Dragan Tutic, Founder and CEO of Oneka Technologies, added that "our mission is to make the oceans an affordable and sustainable source of water."

Solar – low-cost water purification

Solar power has been used to convert saltwater into fresh drinking water , by researchers from King's College in London in collaboration with MIT and the Helmholtz Institute of Renewable Energy Systems.

A set of specialized membranes channel salt ions into a stream of brine, leaving fresh drinkable water. The system adjusts to variable sunlight without compromising the volume of drinking water produced. The process is 20% cheaper than traditional desalination methods, which could boost efforts to provide drinking water in developing countries, the researchers say.

Dutch start-up Desolenator – supported by Uplink, the innovation platform of the World Economic Forum – is also using solar power for its low-cost water-as-a-service model for communities and businesses .

The technology avoids the use of membranes or harmful chemicals, the company says, and customers can choose specific water types to meet their needs: ultra-pure water, pure potable water or customized re-mineralized water.

Each modular plant can produce up to 250,000 litres of freshwater daily, helping boost water security in water-scarce regions.

" We operate with 100% solar power, no harmful chemicals, and now we're building zero liquid discharge, which will make us the first fully circular solar desalination technology in the world," said Desolenator co-founder Alexei Levene.

"We take our waste brine and turn it into salt, so nothing goes back into the environment. It's a distributed technology that we can deploy and it's going to be the most sustainable desalination approach that there is," he said.

Averting a natural resources crisis

A natural resources crisis like water scarcity is listed in the World Economic Forum’s Global Risks Report 2024 , as one of the top 10 threats facing the world in the next decade.

Currently, desalination plants are used in regions like the Middle East, which has a hot climate alongside a buoyant and technologically able economy. But the energy-intensive nature and high costs of conventional desalination plants act as barriers to widespread take-up, the report says.

However, innovations that reduce the energy needed to operate desalination plants and reduce greenhouse emissions from their operations could change the situation and increase access to fresh drinking water for communities facing water challenges.

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Biden-Harris Administration Finalizes First-Ever National Drinking Water Standard to Protect 100M People from PFAS Pollution

As part of the Administration’s commitment to combating PFAS pollution, EPA announces $1B investment through President Biden’s Investing in America agenda to address PFAS in drinking water

April 10, 2024

WASHINGTON - Today, April 10, the Biden-Harris Administration issued the first-ever national, legally enforceable drinking water standard to protect communities from exposure to harmful per-and polyfluoroalkyl substances (PFAS), also known as ‘forever chemicals.’ Exposure to PFAS has been linked to deadly cancers, impacts to the liver and heart, and immune and developmental damage to infants and children. This final rule represents the most significant step to protect public health under EPA’s PFAS Strategic Roadmap . The final rule will reduce PFAS exposure for approximately 100 million people, prevent thousands of deaths, and reduce tens of thousands of serious illnesses. Today’s announcement complements President Biden’s government-wide action plan to combat PFAS pollution.                                                                         

Through President Biden’s Investing in America agenda, EPA is also making unprecedented funding available to help ensure that all people have clean and safe water. In addition to today’s final rule, EPA is announcing nearly $1 billion in newly available funding through the Bipartisan Infrastructure Law to help states and territories implement PFAS testing and treatment at public water systems and to help owners of private wells address PFAS contamination. This is part of a $9 billion investment through the Bipartisan Infrastructure Law to help communities with drinking water impacted by PFAS and other emerging contaminants – the largest-ever investment in tackling PFAS pollution. An additional $12 billion is available through the Bipartisan Infrastructure Law for general drinking water improvements, including addressing emerging contaminants like PFAS.

EPA Administrator Michael Regan will join White House Council on Environmental Quality Chair Brenda Mallory to announce the final standard today at an event in Fayetteville, North Carolina. In 2017, area residents learned that the Cape Fear River, the drinking water source for 1 million people in the region, had been heavily contaminated with PFAS pollution from a nearby manufacturing facility. Today’s announcements will help protect communities like Fayetteville from further devastating impacts of PFAS.

“Drinking water contaminated with PFAS has plagued communities across this country for too long,” said EPA Administrator Michael S. Regan . “That is why President Biden has made tackling PFAS a top priority, investing historic resources to address these harmful chemicals and protect communities nationwide. Our PFAS Strategic Roadmap marshals the full breadth of EPA’s authority and resources to protect people from these harmful forever chemicals. Today, I am proud to finalize this critical piece of our Roadmap, and in doing so, save thousands of lives and help ensure our children grow up healthier.”  

“President Biden believes that everyone deserves access to clean, safe drinking water, and he is delivering on that promise,” said Brenda Mallory, Chair of the White House Council on Environmental Quality . “The first national drinking water standards for PFAS marks a significant step towards delivering on the Biden-Harris Administration’s commitment to advancing environmental justice, protecting communities, and securing clean water for people across the country.”

“Under President Biden’s leadership, we are taking a whole-of-government approach to tackle PFAS pollution and ensure that all Americans have access to clean, safe drinking water. Today’s announcement by EPA complements these efforts and will help keep our communities safe from these toxic ‘forever chemicals,’” said Deputy Assistant to the President for the Cancer Moonshot, Dr. Danielle Carnival . “Coupled with the additional $1 billion investment from President Biden’s Investing in America agenda to help communities address PFAS pollution, the reductions in exposure to toxic substances delivered by EPA’s standards will further the Biden Cancer Moonshot goal of reducing the cancer death rate by at least half by 2047 and preventing more than four million cancer deaths — and stopping cancer before it starts by protecting communities from known risks associated with exposure to PFAS and other contaminants, including kidney and testicular cancers, and more.”

EPA is taking a signature step to protect public health by establishing legally enforceable levels for several PFAS known to occur individually and as mixtures in drinking water. This rule sets limits for five individual PFAS: PFOA, PFOS, PFNA, PFHxS, and HFPO-DA (also known as “GenX Chemicals”). The rule also sets a limit for mixtures of any two or more of four PFAS: PFNA, PFHxS, PFBS, and “GenX chemicals.” By reducing exposure to PFAS, this final rule will prevent thousands of premature deaths, tens of thousands of serious illnesses, including certain cancers and liver and heart impacts in adults, and immune and developmental impacts to infants and children.

This final rule advances President Biden’s commitment to ending cancer as we know it as part of the Biden Cancer Moonshot, to ensuring that all Americans have access to clean, safe, drinking water, and to furthering the Biden-Harris Administration’s commitment to environmental justice by protecting communities that are most exposed to toxic chemicals.

EPA estimates that between about 6% and 10% of the 66,000 public drinking water systems subject to this rule may have to take action to reduce PFAS to meet these new standards. All public water systems have three years to complete their initial monitoring for these chemicals. They must inform the public of the level of PFAS measured in their drinking water. Where PFAS is found at levels that exceed these standards, systems must implement solutions to reduce PFAS in their drinking water within five years.

The new limits in this rule are achievable using a range of available technologies and approaches including granular activated carbon, reverse osmosis, and ion exchange systems. For example, the Cape Fear Public Utility Authority, serving Wilmington, NC – one of the communities most heavily impacted by PFAS contamination – has effectively deployed a granular activated carbon system to remove PFAS regulated by this rule. Drinking water systems will have flexibility to determine the best solution for their community.

EPA will be working closely with state co-regulators in supporting water systems and local officials to implement this rule. In the coming weeks, EPA will host a series of webinars to provide information to the public, communities, and water utilities about the final PFAS drinking water regulation. To learn more about the webinars, please visit EPA’s PFAS drinking water regulation webpage . EPA has also published a toolkit of communications resources to help drinking water systems and community leaders educate the public about PFAS, where they come from, their health risks, how to reduce exposure, and about this rule.

“We are thankful that Administrator Regan and the Biden Administration are taking this action to protect drinking water in North Carolina and across the country,” said North Carolina Governor Roy Cooper . “We asked for this because we know science-based standards for PFAS and other compounds are desperately needed.”

“For decades, the American people have been exposed to the family of incredibly toxic ‘forever chemicals’ known as PFAS with no protection from their government. Those chemicals now contaminate virtually all Americans from birth. That’s because for generations, PFAS chemicals slid off of every federal environmental law like a fried egg off a Teflon pan — until Joe Biden came along,” said Environmental Working Group President and Co-Founder Ken Cook . “We commend EPA Administrator Michael Regan for his tireless leadership to make this decision a reality, and CEQ Chair Brenda Mallory for making sure PFAS is tackled with the ‘whole of government’ approach President Biden promised. There is much work yet to be done to end PFAS pollution. The fact that the EPA has adopted the very strong policy announced today should give everyone confidence that the Biden administration will stay the course and keep the president’s promises, until the American people are protected, at long last, from the scourge of PFAS pollution.”

“We learned about GenX and other PFAS in our tap water six years ago. I raised my children on this water and watched loved ones suffer from rare or recurrent cancers. No one should ever worry if their tap water will make them sick or give them cancer. I’m grateful the Biden EPA heard our pleas and kept its promise to the American people. We will keep fighting until all exposures to PFAS end and the chemical companies responsible for business-related human rights abuses are held fully accountable,” said Emily Donovan, co-founder of Clean Cape Fear.

More details about funding to address PFAS in Drinking Water

Through the Bipartisan Infrastructure Law, EPA is making an unprecedented $21 billion available to strengthen our nation’s drinking water systems, including by addressing PFAS contamination. Of that, $9 billion is specifically for tackling PFAS and emerging contaminants. The financing programs delivering this funding are part of President Biden’s Justice40 Initiative , which set the goal that 40% of the overall benefits of certain federal investments flow to disadvantaged communities that have been historically marginalized by underinvestment and overburdened by pollution.

Additionally, EPA has a nationwide Water Technical Assistance program to help small, rural, and disadvantaged communities access federal resources by working directly with water systems to identify challenges like PFAS; develop plans; build technical, managerial, and financial capacity; and apply for water infrastructure funding. Learn more about EPA’s Water Technical Assistance programs .

More details about the final PFAS drinking water standards:

• For PFOA and PFOS, EPA is setting a Maximum Contaminant Level Goal, a non-enforceable health-based goal, at zero. This reflects the latest science showing that there is no level of exposure to these contaminants without risk of health impacts, including certain cancers.
• EPA is setting enforceable Maximum Contaminant Levels at 4.0 parts per trillion for PFOA and PFOS, individually. This standard will reduce exposure from these PFAS in our drinking water to the lowest levels that are feasible for effective implementation.
• For PFNA, PFHxS, and “GenX Chemicals,” EPA is setting the MCLGs and MCLs at 10 parts per trillion.
• Because PFAS can often be found together in mixtures, and research shows these mixtures may have combined health impacts, EPA is also setting a limit for any mixture of two or more of the following PFAS: PFNA, PFHxS, PFBS, and “GenX Chemicals.”

EPA is issuing this rule after reviewing extensive research and science on how PFAS affects public health, while engaging with the water sector and with state regulators to ensure effective implementation. EPA also considered 120,000 comments on the proposed rule from a wide variety of stakeholders.

Background:

PFAS, also known as ‘forever chemicals,’ are prevalent in the environment. PFAS are a category of chemicals used since the 1940s to repel oil and water and resist heat, which makes them useful in everyday products such as nonstick cookware, stain resistant clothing, and firefighting foam. The science is clear that exposure to certain PFAS over a long period of time can cause cancer and other illnesses.  In addition, PFAS exposure during critical life stages such as pregnancy or early childhood can also result in adverse health impacts.

Across the country, PFAS contamination is impacting millions of people’s health and wellbeing. People can be exposed to PFAS through drinking water or food contaminated with PFAS, by coming into contact with products that contain PFAS, or through workplace exposures in certain industries.

Since EPA Administrator Michael S. Regan announced the PFAS Strategic Roadmap in October 2021, EPA has taken action – within the Biden-Harris Administration’s whole-of-government approach – by advancing science and following the law to safeguard public health, protect the environment, and hold polluters accountable. The actions described in the PFAS Strategic Roadmap each represent important and meaningful steps to protect communities from PFAS contamination. Cumulatively, these actions will build upon one another and lead to more enduring and protective solutions. In December 2023, the EPA released its second annual report on PFAS progress . The report highlights significant accomplishments achieved under the EPA’s PFAS Strategic Roadmap.

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Epa puts limits on 'forever chemicals' in drinking water.

EPA is limiting PFAS chemicals in drinking water in the U.S. Rogelio V. Solis/AP hide caption

EPA is limiting PFAS chemicals in drinking water in the U.S.

The Environmental Protection Agency announced new drinking water standards Wednesday to limit exposure to a class of chemicals called PFAS.

"There's no doubt that these chemicals have been important for certain industries and consumer uses, but there's also no doubt that many of these chemicals can be harmful to our health and our environment," said EPA administrator Michael Regan in a call with reporters.

This is the first time the agency has set enforceable limits on PFAS in drinking water.

PFAS stands for perfluoroalkyl and polyfluoroalkyl substances – a large group of man-made chemicals that have been used since the 1940s to waterproof and stainproof products from clothing, makeup and furniture to firefighting foam and semiconductors.

Manufactured by several large companies including Dupont and 3M, PFAS have strong molecular bonds that don't break down for a long time, which is why they're known as "forever chemicals."

PFAS from the 1940s "are still in our environment today," says Anna Reade , lead scientist on PFAS for the Natural Resources Defense Council. "The levels of these chemicals keep building up in our water and our food and our air."

Evidence for their harmful effects on human health have also accumulated. "Long term exposure to certain types of PFAS have been linked to serious illnesses, including cancer, liver damage and high cholesterol," the EPA's Regan said.

The EPA also noted PFAS exposure has been linked to immune and developmental damage to infants and children.

PFAS 'forever chemicals' are everywhere. Here's what you should know about them

That's why the EPA has finalized a rule restricting six PFAS chemicals in the water – individually, or in combination with each other or both – meaning water systems are required to monitor for these chemicals and remove them if they're found above allowable levels. While some states have instituted their own PFAS limits, this is the first time it's happening on the federal level.

Public water systems will have five years to address their PFAS problems – three years to sample their systems and establish the existing levels of PFAS, and an additional two years to install water treatment technologies if their levels are too high, senior government officials told reporters.

The EPA expects that excess PFAS levels will be found in around 6-10% of water systems, affecting some 100 million people in the U.S.

"This is historic and monumental," says Emily Donovan , co-founder of Clean Cape Fear, an advocacy group working to protect communities from PFAS contamination. "I didn't think [the EPA] would ever do it." Donovan lives in an area of North Carolina which has been contaminated with PFAS from the Chemours chemical manufacturing plant.

She says seeing the EPA set limits is "validating." Six years ago when her group first raised the issue of PFAS, she says they were told that the water met or exceeded state and federal guidelines. "And that's because there weren't any," she says. "It really broke public trust for so many people in our community."

"The final rule is a breakthrough for public health," says Erik Olson, a senior director with NRDC. "We believe it's going to save thousands of lives as a result of reduced exposure of tens of millions of people to these toxic chemicals in the tap water."

There are more than 12,000 known PFAS chemicals. The six that the EPA is restricting "have had many animal and, in many cases, human studies, so [the EPA] feels confident that they have estimated the safe levels of these chemicals," says Elizabeth Southerland, a former EPA official in the Office of Water, who left the agency in 2017.

Southerland says the new limits are a bold first step towards addressing the PFAS problem. And while the EPA has focused on only six chemicals, the treatments that water utilities use to remove these chemicals will also remove other chemicals of concern from drinking water.

In addition to other PFAS, "they will also be taking out all kinds of pesticides, pharmaceuticals and personal care products that are unregulated now under the Safe Drinking Water Act, but [which] we know have serious health effects," Southerland says.

The agency estimates that it will cost $1.5 billion a year for water companies to comply with the regulation – for as long as PFAS continues to show up in the drinking water. "The costs are not just for a one time sampling and then putting in the treatment," Southerland says. They include ongoing monitoring and maintaining equipment, for instance replacing carbon filters on a regular schedule.

The EPA says the benefits will equal, if not exceed the cost, in terms of less cancer, and fewer heart attacks, strokes and birth complications in the affected population.

The announcement comes with $1 billion in grants to help water systems and private well owners conduct initial testing and treatment. It's part of a $9 billion funding package for PFAS removal in the Bipartisan Infrastructure Law . Companies that made these chemicals are also on the hook for more than $10 billion from a class action lawsuit – money which will go to public water systems to remove PFAS.

If water systems can't access those funds, or if the funds run out, some of those costs may eventually get passed on to consumers, says the NRDC's Olson.

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Bottled Water: United States Consumers and Their Perceptions of Water Quality

1 Department of Sociology, Iowa State University, 103 East Hall, Ames, IA 50011, USA; E-Mail: ude.etatsai@notromwl

Lois Wright Morton

Robert l. mahler.

2 PSES Department, University of Idaho, P.O. Box 442339, Moscow, ID 83844, USA; E-Mail: ude.ohadiu@RELHAMB

Consumption of bottled water is increasing worldwide. Prior research shows many consumers believe bottled water is convenient and has better taste than tap water, despite reports of a number of water quality incidents with bottled water. The authors explore the demographic and social factors associated with bottled water users in the U.S. and the relationship between bottled water use and perceptions of the quality of local water supply. They find that U.S. consumers are more likely to report bottled water as their primary drinking water source when they perceive that drinking water is not safe. Furthermore, those who give lower ratings to the quality of their ground water are more likely to regularly purchase bottle water for drinking and use bottle water as their primary drinking water source.

1. Introduction

Consumption of bottled water is increasing by ten percent every year worldwide, with the fastest growth seen in the developing countries of Asia and South America [ 1 ]. The United States (U.S.) is the largest consumer market for bottled water in the world. The U.S. consumption of bottled water in 2008 was estimated to be 8.6 billion gallons, or 27.6 gallons per person [ 2 ]. Despite the common belief that bottled water is safer to drink and has better taste than tap water, scientific studies have shown that the belief is not necessarily true [ 3 , 4 ]. Research also shows that the sales and consumption of bottled water can have environmental and social impacts whose consequences are yet to be fully understood [ 5 – 7 ]. After years of substantial growth in sales, the U.S. bottled water market is recently slowing down. The current economic downturn may have played a part in the drop; however, environmental concern is also an important factor. Some research has found that environmental awareness campaigns may have curbed consumer demand [ 8 – 10 ].

Previous studies about bottled water have focused on its production, regulation, sales and consumption, and criticism and concerns. However, few researchers have examined the relationship between consumer use of bottled water and perceptions of drinking water quality. In this article, the authors explore the demographic and social factors associated with bottled water users in the U.S. and the relationship between bottled water use and perceptions of the quality of local water supply. A brief discussion of bottled water and tap water and bottled water consumers is used to develop several hypotheses. These hypotheses are tested using a national dataset representing twenty-one U.S. states. Results and discussion are followed by implications directed toward educators and public policy makers as they fund and develop programs that promote knowledge about health and local drinking water.

1.1. Bottled Water vs. Tap Water

Bottled water has been used in place of tap water for its convenience, better taste, and perceived purity [ 1 , 3 , 11 ]. Perceptions of bottled water being of higher quality, however, are challenged by the increasing number of water quality incidents with bottled water [ 12 ]. A study showed that only five percent of the bottled water purchased in Cleveland, Ohio had the required fluoride recommended by the state, whereas the sampled tap water 100% met this requirement [ 3 ]. The same experiment also conducted bacteria count on both bottled water and tap water samples. The result showed that all of the tap water samples had a bacterial content under 3 CFUs/mL (colony-forming unit, a measure of viable bacterial or fungal numbers) and the bottled water samples' bacterial content ranged from 0.01–4,900 CFUs/mL. Although most of the water bottle samples were under 1 CFU/mL, there were 15 water bottle samples containing 6–4,900 CFUs/mL [ 3 ]. Another study focusing on the temperature and duration of storage for bottle water found that the bacterial growth in bottled water was markedly higher than that in tap water, especially at higher temperatures [ 4 ].

Many scientific reports on bottled water urge increased public awareness and development of guidelines/regulations on the industry of bottled water [ 1 ]. Incidents with bottled water quality are largely reported as associated with lenient regulations on bottled water. Bottled water plants are subject to the U.S. Food and Drug Administration (FDA) monitoring and inspection. Despite specific inspection requirements, bottled water plants are given low priority for safety inspection compared with other food plants because of FDA’s staffing and financial constraints [ 13 ]. The “Nutrition Facts” label on bottled water usually shows only limited information about the water [ 1 ].

Despite the popularity of bottled water in the U.S., there are a number of environmental and social concerns. Plastic bottles are a waste problem adding to landfill overload when not recycled. Water bottling plants have impacts on local groundwater aquifers and streams [ 5 ]. Taking too much water can reduce or deplete groundwater reserves and reduce the flow of streams and lakes, causing stress on ecosystems. Although 75% of the world bottled water is produced and distributed on a regional scale, trading and transporting the other 25% bottled water also raises the concern for pollution and carbon dioxide emission [ 6 ]. The price of bottled water is on average 500 to 1,000 times higher than that of tap water [ 6 ], contributing to concern for affordable access to drinking water. Limited resource populations that use bottled water for drinking are least able to afford the high cost associated with bottled water [ 1 ]. Another issue associated with increased consumption of bottled water is that it can erode public tap water revenues and the capacity of governments to provide necessary improvements in basic water infrastructure [ 7 ].

1.2. Consumers of Bottled Water

Eighty-five million bottles of water are consumed in the United States every day and more than thirty billion bottles a year [ 14 ]. The adoption of a health preventive action like drinking bottled water is suggested to be influenced by perception of risk associated with drinking water [ 15 ]. The perception of risk is also thought to be closely related to the subjective assessment of drinking water quality [ 11 ]. This suggests that perceptions of drinking water safety and beliefs about the ground and surface water quality in a local area might be explanatory factors for a decision to select bottled water over tap water.

Another safety factor influencing consumer decision to select bottled water over tap water is the type of water supply system where the consumer lives. Small water systems (small town, tribal system, rural water district) [ 16 ] in the U.S. were found to have problems complying with federal/state quality standards. According to one study, due to inadequate funding and facilities, small water systems reportedly violated federal drinking water regulations more frequently than larger ones [ 11 ]. Although the number of public water consumers whose water does not meet current standards has decreased significantly over years, the task of water regulation is still challenging given both the financial limitations and increasing public concern about their drinking water [ 11 ].

Socio-economic status is also a factor affecting consumer decisions, particularly given the high cost associated with bottled water. Gender and education differences have been found to affect preference of bottled water over tap water because of their noted differences in perception of environmental risk [ 11 , 17 ].

Risk perception and preventive behaviors are the result of complicated social, cultural, and psychological factors as well as objective information [ 18 ]. This suggests that because of the differences in economic, social, and environmental contexts, residents of different regions might have different attitudes towards bottled water. In an earlier study, the findings showed that people in the Pacific region had more per capita consumption of bottled water than in other places of the U.S. [ 11 ]. In this article, the regional factor is examined and the popularity of bottled water is mapped across geographic regions.

2. Experimental Section

2.1. hypotheses.

Prior studies of bottled water consumption have identified a variety of explanatory factors for consumption behavior. However, these factors have not been considered together in one single model. For example, the regional differences found between the Pacific and the rest parts of the U.S. might be due to confounding factors such as differences in community size, local water quality problems, or water supply systems. Therefore, we propose to test these variables of interest simultaneously using a logistic regression. Hypotheses regarding use of bottled water are as follows:

• H1: Perceptions of poorer groundwater and surface water quality represent higher risk in drinking water and therefore are hypothesized to be associated with higher likelihood of purchasing bottle water as a primary drinking source compared to those reporting perceptions of higher water quality. Related, perceptions that drinking water is not safe are associated with higher likelihood of purchasing bottled water for drinking as a primary water source.
• H2: Based on the observations about small water supply systems, we hypothesize that small water supply (community well and rural district) users are more likely to use bottled water for drinking compared to public municipal water supply users. Community size is used as a control variable.
• H3: Because of the environmental impact associated with bottled water, we test the association between environmental attitudes and bottled water use. The association between the two is hypothesized to be that the more pro-environmental views a person holds, the less likely the person frequently uses bottled water for drinking.
• H4: We hypothesize a regional effect on the use of bottled water, although the specific pattern about such regional differences is not clear at this stage.

Other variables tested in the logistic model include age, education, and gender.

2.2. Methodology

Data used for this study were collected from a national stratified random sample mail survey about water issues conducted by Dr. Robert Mahler of University of Idaho. Our analysis used data from twenty-one states, which partially cover five out of the ten U.S. EPA water regions [ 19 ]. Data were collected 2004 through 2009 (region 8 and 9, 2004; region 7, 2006; region 6, 2008; and region 4, 2009). Sample sizes for each state were calculated based on the state population and targeted sampling error of four to six percent, with anticipation that the return rate would exceed fifty percent [ 20 ]. In each individual state, samples were either randomly selected from phone books or obtained from a professional social sciences survey company (Survey Sampling International, Norwich, Connecticut). The questionnaires were pilot tested, revised, and then mailed to sampled names and addresses. The final sample size was 5,823. Standard mail survey methods [ 21 ] were followed in all the regions and institutional review board (IRB) approval was obtained from University of Idaho Office of Research Assurance prior to the survey process. Response rates of each state ranged from 37% to 70%, with median return rates reaching the targeted 50%. The questionnaires, generally about 50 questions, varied in their content and wording due to the regions’ differing priorities. However, there were a number of core questions that all states asked. It is these questions in common that make up our data set. These core survey items asked about respondents’ perceptions of water quality, use of bottled water, water supply type, general environmental attitudes, and demographic information.

Two sources of drinking water questions were of interest in this study. The first one was “where do you primarily get your drinking water.” Possible responses to this question included: private supply (private well, river, pond, lake, etc. ), public municipal supply, small water supply systems (including rural water district and community well), and purchase bottled water. If respondents chose “purchase bottled water” for this question, they were identified as primary users of bottled water.

The second question asked if the respondent “often use bottled water for drinking purposes.” If respondents answered “yes” to this question, they were labeled as regular users of bottled water. The above two questions were not mutually exclusive, which means that a primary bottled water user may be a regular bottled water user.

First, we tested hypotheses one, three and four on the primary bottled water users using a logistic regression model. The independent variables used in this logistic regression were as follows:

Surface and ground water quality perceptions. Respondents were asked to rate the surface and ground water quality in their area. Responses were coded 1 = poor, 2 = fair, 3 = very good/excellent.

Drinking water safety. The original question asked if the respondents felt their home drinking water is safe to drink. Response options were 0 = no, and 1 = yes.

Environmental attitudes . Respondents were asked to indicate where they stand on environmental issues by placing a mark on a line with numbers 1 to 10, where 1 represented preference for total natural resource use and 10 represented preference for total environmental protection.

Community size. Community size was measured by asking respondents to choose from the options which best described their community size, although no strict definition was given to the term “community”. Community sizes were measured with five categories. 1 was “less than 3,500 people”; 2 = “3,500 to 7,000”; 3 = “7,000 to 25,000”; 4 = “25,000 to 100,000”, and 5 was “more than 100,000.”

Age and gender . Age was a continuous variable measuring the ages of respondents, and gender was recorded as 0 = female and 1 = male.

Education . Five categories of formal education levels were provided to choose from, ranging from “less than high school” to “advanced degree.”

Residence region . The two bottled water questions of interest were asked in the following regions and states, which include several states of the southeast region (Region 4: Alabama, Florida, Mississippi, Tennessee); the southern region (Region 6: Arkansas, Louisiana, Oklahoma, Texas); the Midwest Heartland region (Region 7: Iowa, Kansas, Missouri, Nebraska); the mountain region (Region 8: Colorado, Montana, North Dakota, South Dakota, Utah, Wyoming); and the southern Pacific region (Region 9: Arizona, California, Nevada [ 22 ]). Figure 1 gives a visualization of the above states and regions.

Map of the Sampled Regions and States.

Secondly, we applied a logistic regression on the regular bottled water users. With this part of analysis, we focused on the respondents who used sources other than bottled water for primary drinking purposes but reportedly often used bottled water for drinking. The hypothesis to be tested with this model is the second one, and the independent variable of primary interest is water supply type, which has three categories: 1 = private supply (private well, river, pond, lake, etc. ), 2 = public municipal supply, and 3 = small water supply systems (including rural water district and community well). All the other independent variables used in the previous model were also included in this logistic regression model.

3. Results and Discussion

3.1. descriptive summary of the sample.

The demographic distribution of survey respondents was similar to that reported for the general adult population based on the 2000 US census data for the demographic factors of community size, age (adult population), and formal education level. The only factor not in line with 2,000 census data was gender. Here, male respondents were much more heavily represented compared to the general population as a whole (about two thirds of the respondents were male, see Table 1 ). Even though 50% of the mailed surveys were addressed to females, it was apparent that the male adult in the surveyed household was more likely to respond to the survey [ 20 ]. The summary of sample statistics is shown in Table 1 below.

Summary Statistics.

Over 13% of all respondents reported that they used bottled water as the primary source for drinking water, while 45.4% of all respondents said they often used bottled water for drinking. The mean for surface water quality perception was 1.99 (fair), and the mean for ground water quality perception was 2.22 (slightly above fair), a little higher than that of surface water. About fifteen percent respondents said they felt their home drinking water was not safe to drink. This percentage corresponded well to the percentage of respondents that used bottled water as their primary drinking source. On a scale of 1 to 10, average environmental attitude score was 5.76, and responses tended to cluster in the middle of the 1 to 10 scale. Thirty-five percent respondents marked their environmental view as 5, midway between totally eco-centric and totally anthropocentric. Other responses with higher percentage are 4 (9%), 6 (15%), and 7 (16%). About 12% respondents responded with higher scores (8–10), and the lower extreme scores (1–3) are only 6% of the total responses. This represents a balanced, somewhat more pro-environmental view towards the relationship between protection of nature and human use of natural resources. Mean age of the survey respondents was 56.8, while average formal educational achievement was between “some college” and “college degree.” About two thirds of the respondents were male.

3.2. Logistic Regression Model 1: Primary Bottled Water Users

Our first model used a logistic regression model to examine the relationship between primary bottled water users and water quality perceptions ( Table 2 ).

Logistic Regression for primary bottled water users (N = 3,232).

We found that groundwater quality perception was a significant predictor. As the ground water quality perception increased by one ascending-ordered category, the odds of a person using bottled water as primary source of drinking water was reduced by 33%. Compared with a person who feels their home water is safe to drink, a person who does not trust their home drinking water safety was more than 4.8 times more likely to use bottled water as their primary source of drinking water. However, there was no significant difference in bottled water use among respondents with different surface water quality perceptions. Environmental attitudes were not a significant predictor for primary bottled water use.

Age and gender were also found to be significant predictors for bottled water use. When all other conditions were exactly equal, a respondent who was one year older in age was about 2% less likely to use bottled water as the primary source of drinking water. From a gender standpoint, the odds that a female uses bottled water for primary drinking source are 1.32 times as much as the odds for a male, with all other conditions being equal. Education level was not a significant predictor for bottled water use.

Place of residence was found to have important effect on the use of bottled water. For example, community size had a positive relationship with being a primary bottled water user. As the community size increased by one ascending category, the odds of the resident of larger community using bottled water for primary drinking purposes were increased by 0.116 times. The use of bottled water as primary source of drinking water was also closely related to where the respondents lived in the U.S. For example, a respondent in the Midwest (region 7), when compared with a respondent living in the southern Pacific region (region 9), was over 80% less likely to be a primary user of bottled water. Similarly, for a respondent in the mountain region (region 8), the odds of the person using bottled water as primary drinking water source were reduced by 53% compared with a resident in the southern Pacific region (region 9). Similar to the southern Pacific region (region 9), the southern region (region 6) and the southeast region (region 4) also have more residents primarily depending on bottled water for drinking (see appendix for detailed regional bottled water use comparison).

With logistic regression models, there is no equivalent r-squared statistics to show the explained variability in the dependent variable. However, the pseudo R 2 shows that the explanatory variables have moderate strength of associations with consumption of bottled water. The model non-significant chi-square test and likelihood ratio test statistics (1.0), which suggests good model fit [ 23 ].

Overall, this model shows that U.S. consumer perceptions about groundwater quality have strong associations on the purchase of bottled water for drinking. This suggests that bottled water use may be considered a substitute for other water sources when groundwater quality is perceived to be poor.

3.3. Logistic Regression Model 2: Regular Bottled Water Users

A second logistic regression model was used to predict regular users of bottled water ( Table 3 ).

Logistic Regression for regular bottled water users (N = 2,850).

These results show similar patterns as with primary bottled water users found in Table 2 . Groundwater quality perception, safe drinking water perception, age, gender, and region of residence were found to be significant predictors. Community size, however, unlike in the first regression model, was not significant. The likelihood of private water supply users being regular bottled water users was about 25% less than that of small water supply system users. There were no significant differences in bottled water use between municipal water supply users and small water supply system users.

The pseudo r-squared statistics are relatively small compared with our first model, which suggests that the same independent variables do not have particularly strong correlations with or explaining power for regular bottled water usage, although the chi-square test statistic is still non-significant.

3.4. Discussion

With findings of both logistic models, we confirmed the hypothesized negative association between perception of ground water quality and bottled water use. Given that an estimate of 49% of the U.S. population depends on groundwater for its drinking water supply from either a public source or private well [ 24 ], the groundwater quality perception seems to explain the consumers’ behavior regarding bottled water. Perception of drinking water safety is found to be highly associated with bottled water use. The findings about water quality perceptions generally confirmed that when public doubts about the safety of their tap water, they look for alternatives like bottled water [ 6 , 14 ]. No significant relationship, however, was found between surface water quality perception and bottled water use.

Our data do not include actual water quality or safety conditions so it is not known whether consumer’s perceptions of the condition of their local drinking water are accurate reflections of the real water quality or not. If perceptions are accurate, then community leadership along with regulatory agencies needs to act to correct the problems for public health to be maintained. However, one might ask why consumers have turned to bottled water purchases rather than voice their concern and pressure public water departments and elected officials for solutions. This is particularly relevant since it is public municipal and rural water system supply users rather than private water supply users that are likely to purchase bottled water. Public water systems are tax supported, regulated and maintained under much more rigorous monitoring and testing conditions than bottled water manufacturers. This suggests that if a large number of consumers purchase drinking water as a substitute for public tap water, they can undermine the water infrastructure investments needed to assure safe public water supplies. This has implications for community capacities to provide low cost, accessible, and safe drinking water for their entire population. Without safe public water supplies, limited income households’ health and well-being are at risk.

Our findings show that although municipal water supply users and small water supply users were equally likely to be regular bottled water users when every other condition is held the same, private water supply users (private well or surface water sources) were less likely to use bottled water than small water supply users. Consumers on private wells are often targets of public health campaigns reminding them to have their water tested regularly. To the extent this happens, private water supply users may believe they have more knowledge of and control over the quality of their water supply and thus trust it. Also, media coverage and increased headlines concerning problems with public water systems around the world can lead to high distrust (appropriately) of local water supplies [ 14 ]. The poor water conditions also increase the cost of treating water in public systems so that it is safe for consumption. This can lead to changes in water taste despite being safe to drink after treatments. While substituting bottled water for public tap water under these circumstances may be a short term “fix”, it does not address long term problems of water quality or the effect it has on escalating the cost of public water as increased treatments become necessary.

Residents of larger communities were found to be more likely to be primary bottled water users, which means that a higher proportion of population in larger communities tend to depend on bottled water rather than their tap water for drinking purpose. Note that this association is established when other conditions are controlled for. That is, for two persons in the same region, with the same perceptions towards their drinking water, surface and ground water quality, and having exactly the same demographic characteristics (age, gender, education), the person from larger community is more likely to depend on bottled water for drinking purpose. As some researchers have suggested, factors like media hype about water supply problems, commercial campaigns on bottled water, or even peer pressure for more fashionable ways of drinking all contribute to bottled water consumption [ 6 , 14 ]. And considering that these factors are usually stronger in larger cities, it is likely that people in larger cities have more negative feelings about their water supply systems and turn to bottled water for solution. However, if respondents were already using some sort of water supply for drinking purpose, then there is no significant association found between their community size and whether or not they regularly consume bottled water. With limited information in our data we were not able to fully explain the associations found between community size and bottled water consumption, and we suggest future research look at community level variables for possible answers.

Our data also show that younger people and females are more likely to purchase bottled water. Young people are generally believed to be more susceptible to marketing and advertising, which are essential keys held by the bottled water companies [ 6 , 14 ]. And the higher likelihood of female drinking bottled water is consistent with previous literature on gender differences in risk, especially health and food related risk perceptions [ 25 , 26 ]. The findings about more consumption in these two groups of people suggests a need to target these audiences with messages about the importance of learning about their local water quality as well as the costs and quality differences between bottled water and public drinking water supplies.

Our hypothesis about environmental attitudes was not supported by the data. The relationship between environmental attitudes and bottled water use was not significant. Consumers with stronger overall concern about the environment do not seem to transfer this concern to pollution and waste problems associated with purchasing bottled drinking water. But again, because of the relatively longer cycle of research using multistate data (data collection in some states were done back in 2004), our data might not be able to reflect the newest trend of national environmental concern on bottled water.

Finally, the hypothesized regional effect regarding bottled water use was confirmed by the data. Residents of the Midwest and west mountain regions were far less likely to use bottled water for either primary drinking purpose or other occasions of regular uses, while residents of the southern pacific, the south, and the southeast were all equally likely to be bottled water users. This suggests that other variables such as culture, actual water quality conditions, media coverage of water issues and other place specific factors may be influencing the decision to use bottled water versus tap water from a private or public system. Water resource quantity and income might also be driving forces for the differences. Further research is needed to better explain regional variations.

4. Conclusions

Water is essential to human health and life. Access to safe water supplies and affordability are central concerns of public health and individual consumers. In this study we find that perceptions of ground water quality and local water supply safety are associated with decisions to purchase bottled water versus use public water systems for drinking water. When local water is not considered safe or of high quality U.S. consumers are more likely to use bottled water as a primary water source. Furthermore, negative perceptions of safety increase the likelihood of a consumer frequently purchasing bottled water regardless of whether their primary source of drinking water is a small water system or large municipal water supply system.

Two key implications of our findings are that (1) public health officials and community leaders need to work to assure that public municipal drinking water supplies are safe; in addition, they should find effective ways to communicate to local residents the safety of their water supply; and (2) environmental leaders and activists need to campaign about the long lasting impacts of plastic water bottles. Further the public must be engaged in understanding the relationship of water quality to the capacity of local water systems to maintain safety and good taste standards. Consumer distrust of their groundwater quality should be leveraged to create community action to address legitimate concerns.

Acknowledgments

This research was partially funded by the National Institute of Food and Agriculture (NIFA), U.S. Department of Agriculture (USDA) under agreement 2008-51130-19526 also known as the Heartland Regional Water Coordination Initiative, the Iowa Agriculture and Home Economics Experiment Station, and USDA agreement 2008-51130-0474, also known as the Pacific Northwest Regional Water Resources Coordination Project.

A separate analysis, a one-way ANOVA (analysis of variance) was done to compare regional differences in bottled water use for primary drinking purposes. Table 1 shows bottled water use in each region and differences with statistical significance. The variable (primarily purchase bottled water for drinking) is a dichotomous variable with two possible responses 0 (not purchase) and 1 (purchase bottled water for drinking). Therefore the following means reflect proportion of respondents responding with 1 in each region. Post-hoc Bonferroni pair tests were conducted on the means and the last column of the following table shows regions with significant differences (at 0.05 level). For example, the first row shows that region 4 has mean which is significantly different from that of region 6, 7, 8, and 9, respectively.

Bottled water use by region.

Region 9 and region 6 have significantly higher percent of primary bottled water users, followed by region 4. Region 7 and region 8 have the least primary bottled water users.

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Biden administration sets first-ever limits on ‘forever chemicals’ in drinking water

Logan Feeney pours a PFAS water sample into a container for research, Wednesday, April 10, 2024, at a U.S. Environmental Protection Agency lab in Cincinnati. The Environmental Protection Agency on Wednesday announced its first-ever limits for several common types of PFAS, the so-called “forever chemicals,” in drinking water. (AP Photo/Joshua A. Bickel)

Vials containing PFAS samples sit in a tray, Wednesday, April 10, 2024, at a U.S. Environmental Protection Agency lab in Cincinnati. The Environmental Protection Agency on Wednesday announced its first-ever limits for several common types of PFAS, the so-called “forever chemicals,” in drinking water. (AP Photo/Joshua A. Bickel)

FILE - Environmental Protection Agency Administrator Michael Regan speaks at the University of Maryland on May 11, 2023, in College Park, Md. The Environmental Protection Agency announced, Wednesday, April 10, 2024, its first-ever limits for several common types of PFAS, the so-called “forever chemicals,” in drinking water. (AP Photo/Nathan Howard, File)

Jackson Quinn brings PFAS water samples into a temperature controlled room, Wednesday, April 10, 2024, at a U.S. Environmental Protection Agency lab in Cincinnati. The Environmental Protection Agency on Wednesday announced its first-ever limits for several common types of PFAS, the so-called “forever chemicals,” in drinking water.(AP Photo/Joshua A. Bickel)

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The Biden administration on Wednesday finalized strict limits on certain so-called “forever chemicals” in drinking water that will require utilities to reduce them to the lowest level they can be reliably measured. Officials say this will reduce exposure for 100 million people and help prevent thousands of illnesses, including cancers.

The rule is the first national drinking water limit on toxic PFAS, or perfluoroalkyl and polyfluoroalkyl substances, which are widespread and long lasting in the environment.

Health advocates praised the Environmental Protection Agency for not backing away from tough limits the agency proposed last year . But water utilities took issue with the rule, saying treatment systems are expensive to install and that customers will end up paying more for water.

Water providers are entering a new era with significant additional health standards that the EPA says will make tap water safer for millions of consumers — a Biden administration priority. The agency has also proposed forcing utilities to remove dangerous lead pipes .

Utility groups warn the rules will cost tens of billions of dollars each and fall hardest on small communities with fewer resources . Legal challenges are sure to follow.

EPA Administrator Michael Regan says the rule is the most important action the EPA has ever taken on PFAS.

“The result is a comprehensive and life-changing rule, one that will improve the health and vitality of so many communities across our country,” said Regan.

PFAS chemicals are hazardous because they don’t degrade in the environment and are linked to health issues such as low birth weight and liver disease, along with certain cancers. The EPA estimates the rule will cost about $1.5 billion to implement each year, but doing so will prevent nearly 10,000 deaths over decades and significantly reduce serious illnesses.

They’ve been used in everyday products including nonstick pans, firefighting foam and waterproof clothing. Although some of the most common types are phased out in the U.S., others remain. Water providers will now be forced to remove contamination put in the environment by other industries.

“It’s that accumulation that’s the problem,” said Scott Belcher, a North Carolina State University professor who researches PFAS toxicity. “Even tiny, tiny, tiny amounts each time you take a drink of water over your lifetime is going to keep adding up, leading to the health effects.”

PFAS is a broad family of chemical substances, and the new rule sets strict limits on two common types — called PFOA and PFOS — at 4 parts per trillion. Three other types that include GenEx Chemicals that are a major problem in North Carolina are limited to 10 parts per trillion. Water providers will have to test for these PFAS chemicals and tell the public when levels are too high. Combinations of some PFAS types will be limited, too.

Regan will announce the rule in Fayetteville, North Carolina, on Wednesday.

Environmental and health advocates praised the rule, but said PFAS manufacturers knew decades ago the substances were dangerous yet hid or downplayed the evidence. Limits should have come sooner, they argue.

“Reducing PFAS in our drinking water is the most cost effective way to reduce our exposure,” said Scott Faber, a food and water expert at Environmental Working Group. “It’s much more challenging to reduce other exposures such as PFAS in food or clothing or carpets.”

Over the last year, EPA has periodically released batches of utility test results for PFAS in drinking water. Roughly 16% of utilities found at least one of the two strictly limited PFAS chemicals at or above the new limits. These utilities serve tens of millions of people. The Biden administration, however, expects about 6-10% of water systems to exceed the new limits.

Water providers will generally have three years to do testing. If those test exceed the limits, they’ll have two more years to install treatment systems, according to EPA officials.

Some funds are available to help utilities. Manufacturer 3M recently agreed to pay more than $10 billion to drinking water providers to settle PFAS litigation. And the Bipartisan Infrastructure Law includes billions to combat the substance. But utilities say more will be needed.

For some communities, tests results were a surprise. Last June, a utility outside Philadelphia that serves nearly 9,000 people learned that one of its wells had a PFOA level of 235 parts per trillion, among the highest results in the country at the time.

“I mean, obviously, it was a shock,” said Joseph Hastings, director of the joint public works department for the Collegeville and Trappe boroughs, whose job includes solving problems presented by new regulations.

The well was quickly yanked offline, but Hastings still doesn’t know the contamination source. Several other wells were above the EPA’s new limits, but lower than those the state of Pennsylvania set earlier. Now, Hastings says installing treatment systems could be a multi-million dollar endeavor, a major expense for a small customer base.

The new regulation is “going to throw public confidence in drinking water into chaos,” said Mike McGill, president of WaterPIO, a water industry communications firm.

The American Water Works Association, an industry group, says it supports the development of PFAS limits in drinking water, but argues the EPA’s rule has big problems.

The agency underestimated its high cost, which can’t be justified for communities with low levels of PFAS, and it’ll raise customer water bills, the association said. Plus, there aren’t enough experts and workers — and supplies of filtration material are limited.

Work in some places has started. The company Veolia operates utilities serving about 2.3 million people across six eastern states and manages water systems for millions more. Veolia built PFAS treatment for small water systems that serve about 150,000 people. The company expects, however, that roughly 50 more sites will need treatment — and it’s working to scale up efforts to reduce PFAS in larger communities it serves.

Such efforts followed dramatic shifts in EPA’s health guidance for PFAS in recent years as more research into its health harms emerged. Less than a decade ago, EPA issued a health advisory that PFOA and PFOS levels combined shouldn’t exceed 70 parts per trillion. Now, the agency says no amount is safe.

Public alarm has increased, too. In Minnesota, for example, Amara’s Law aims to stop avoidable PFAS use. It’s been nearly a year since the law’s namesake, Amara Strande, died from a rare cancer her family blames on PFAS contamination by 3M near her high school in Oakdale, although a connection between PFAS and her cancer can’t be proven. Biden administration officials say communities shouldn’t suffer like Oakdale. 3M says it extends its deepest condolences to Amara’s friends and family.

Losing Amara pushed the family towards activism. They’ve testified multiple times in favor of PFAS restrictions.

“Four parts per trillion, we couldn’t ask for a better standard,” Amara’s sister Nora said. “It’s a very ambitious goal, but anything higher than that is endangering lives.”

Associated Press data journalist Camille Fassett in San Francisco and reporter Matthew Daly in Washington D.C. contributed to this story.

The Associated Press receives support from the Walton Family Foundation for coverage of water and environmental policy. The AP is solely responsible for all content. For all of AP’s environmental coverage, visit https://apnews.com/hub/climate-and-environment