These analyses of total water intakes from all sources, including tap and bottled water, were conducted among a representative sample of US children age 4-13y from 2005–2010 NHANES. The amounts of dietary water provided by plain water and by other beverages and foods were compared to AI values by gender and age group. The intent was to examine how close children and adolescents came to meeting the AI values, as defined by the IOM DRIs. According to the IOM, AI values may be used as goals for individual intakes , though there is much inter-individual variation. Water needs can be influenced by health status; physical activity or strenuous work; dietary factors, including sodium and protein intake; and environmental factors, such as temperature and humidity [2, 10, 12, 21–23]. These additional factors need to be considered when evaluating adequate intakes at the individual level.
The majority of girls (83%) and boys (85%) age 9-13y failed to meet the IOM DRI value. Children aged 4-8y consumed about 15% less water on the average than the IOM DRIs and at least 75% failed to meet the IOM DRIs for water. Girls aged 9-13y were 444 mL/d short of meeting the IOM DRI recommendations for water, whereas boys aged 9-13y were 633 mL short. EFSA provides additional recommendations for total water intake, which are marginally different from the IOM DRI values (e.g., 1,600 mL/d for children 4-8y based on EFSA compared to 1,700 mL/d based on IOM DRIs) . We conducted secondary analyses using the EFSA values. At least 72% of children age 4-13y failed to meet the EFSA guidelines. At least 69% of children 4-8y, 73% of girls 9-13y and 75% of boys 9-13y failed to meet the EFSA recommendations. The second criterion of adequate hydration, water volume per 1,000 kcal also fell short of desirable values. Whereas the standard IOM recommendation is at least 1.0 L per 1,000 kcal , the observed values were in the 0.85-0.95 L range, depending on age and gender.
Urine osmolality is another measure of adequate hydration, but it was obtained for only 1 cycle of NHANES data (2009–2010) and not evaluated in the present study . A recent study of 548 children age 9-11y showed elevated urine osmolality (an index of hyperosmotic cell shrinkage) in more than 63% of schoolchildren in Los Angeles and New York . Elevated urine osmolality was associated with not drinking water in the morning prior to going to school. Although 90% of the children had breakfast, 75% did not drink water at breakfast. A majority of participants (value not provided in the paper) reported consuming any food or a beverage other than water at the morning meal .
The present analyses of the observed water intakes relative to the indices of hydration suggest that children’s water consumption ought to be monitored more closely . In 2010, EFSA published a 48 page report on water consumption alone , arguing that water is often disregarded in national and international recommendations or is very cursorily treated . For example, the 2010 US Dietary Guidelines devoted only two pages to water, stating that most healthy people consumed adequate water to meet their needs . Because water needs vary considerably by individual characteristics, the Dietary Guidelines Advisory Committee concluded that a minimum intake of water could not be set .
The present study provides valuable new data on children’s consumption of plain drinking water and other beverages. The data on water consumption by socio-demographic group may be useful in identifying population sub-groups that may benefit from targeted interventions to increase total water intake. The evaluation of tap versus bottled water by population sub-group provides additional data to support potential intervention strategies. Past studies have tended to focus on the contribution of beverages to energy and nutrient intakes, focusing variously on milk , fruit juices, and sweetened beverages [29, 30]. In some cases, the consumption of caloric beverages was related to the children’s body weight . Other studies  have made the point that some of the nutrient-poor beverages that the children were consuming could be replaced with more nutrient-dense options such as low-fat and fat-free milk.
Given the dearth of recent data on water and beverage consumption among US children, the present study fills a gap in the existing knowledge on water consumption patterns among US youth. As yet, there are no clear recommendations on the desirable water volumes per 1,000 kcal for children and adolescents. The scientific evidence cited in the 2010 Dietary Guidelines Advisory Committee Report referenced data from NHANES III showing that fluids provided 3.0 L/day for men and 2.3 L/day for women aged 19-30y . Whereas fluids provided approximately 81% of total water intake, moisture in food provided the remaining 19%. Child-specific data were not provided.
Future guidelines on beverage consumption for children should take plain drinking water into account. This is particularly important given the size of the shortfall between observed intakes and DRI reference values. Total water intake can be increased in a number of ways. The most effective way would be to increase the consumption of plain water, either tap or bottled. In addition to promoting skim and low-fat milk consumption, the USDA now requires schools participating in the National School Lunch program to make free potable water available to students when meals are served [31–33]. In addition, as numerous recommendations to reduce intake of caloric beverages have emerged [26, 34, 35], it will be important to carefully monitor total water intake to determine if such policies and interventions may have a deleterious impact on total water intake.
In the present analyses of NHANES 2005–2010 data, non-beverage food sources accounted for 25-30% of total dietary water for most population groups, as opposed to 19% from previous reports . Increasing consumption of low-energy-density foods with high water content (e.g., fruits/vegetables) is another way to increase water intakes. However, a modest increase in fruit and vegetable consumption is unlikely to have a major impact on adequate hydration; drinking water and beverages are more effective strategies.
It is important to mention that these data cannot be directly compared to those from cycles of NHANES prior to 2005, as the method for collecting water intake data has changed. Prior to 2005, water intake was measured after the dietary recall was completed. In more recent cycles (2005 onward), water was reported during the 24-hour recall in the same manner that any other food/beverage was reported [18–20]. Comparisons of water intake for the total adult population and adult population sub-groups from 1999–2004 and 2005–2006 reveal that estimated water intakes are generally 15% lower when comparing new (2005–2006) to old data (1999–2004) . While this difference may be attributable to secular changes in water intake, they may also be explained by changes in data collection. It is unclear which approach is most valid for assessing water intake, but caution should be applied when comparing the results presented here to data collected prior to 2005, especially in interpreting whether children or any group consume less water now (2005–2010) than in the past. Given these issues, the work presented here focuses on comparisons between groups of children and to established reference values, as opposed to an evaluation of trends in water intake.
The present analyses had limitations. First, the NHANES data are based on self-report and are subject to random and systematic reporting errors. Proxy recall for younger children may be an additional source of error. Different diet recall methods used to collect the data (first day in-person and second day over the telephone many days later) may introduce mode effects into the estimate of water consumption. If water intakes were under-reported in the NHANES database, then the estimates presented here will over-estimate the percent of adults who fail to meet the recommended intakes. It is possible that many respondents under-reported water intakes due to drinking water events lacking saliency. This may be particularly problematic for events where little water was consumed (e.g., stopping at a drinking fountain) or when it was consumed casually without active choices being made by participant (e.g., repeatedly being refilled at a restaurant). As noted previously, since methods for data collection have changed the results presented here cannot be directly compared to those from previous cycles of NHANES. Despite these limitations, these data have a number of advantages as they represent a large, nationally representative data source that forms the basis for dietary surveillance in the US.