These analyses of total water intakes from all sources, including tap and bottled water, were conducted among a representative sample of US adults from the NHANES 2005–2010 database. The amounts of dietary water provided by plain water and by other beverages and foods were then compared to AI values by gender and by age group. The intent was to examine how close the population 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 for water needs. Health status, physical activity or strenuous work, and environmental factors, such as temperature and humidity, are additional aspects to be considered when evaluating adequate intakes at the individual level
[2, 13, 30–32].
A large proportion of older men (94.7%) and women (82.6%) failed to meet the IOM AI values. The average shortfall was 1218 mL (41.2 fl oz) for older men and 603 mL (20.4 fl oz) for older women. The average shortfall was only 122 mL (4.1 fl oz) for men 50–70, though 59.1% consumed less than 3700 mL per day. Although the average intake of water among women less than 70 was adequate; 45% and 41% of women 51-70y and 20-50y consumed less than 2700 mL of water per day. Younger men consumed the most total water, but 42.7% consumed less than 3700 mL of water per day.
The second criterion of adequate hydration, water volume (in mL) per 1000 kcal, did not fall short of desirable values, though such an evaluation is dependent on measuring energy intakes and expenditures accurately. Whereas the EFSA and IOM recommendations are at least 1.0 L per 1,000 kcal
[10, 13], the observed values of ~1.2-1.4 L/1,000 kcal were well above this cut-point, though there were some differences by population sub-group. Women, non-Hispanic whites and adults with higher family incomes tended to have diets that were more water dense.
The evaluation of water density suggests that water intake at the population-level is generally adequate, though evaluations of absolute values suggest that water intake may be too low among older adults. It is beyond the scope of this work to identify which of these two measures is the better indicator of water intake. Given the focus of the IOM DRIs Committee on the absolute intakes and the potential for under-estimating energy expenditure/intake, more emphasis should be placed on the absolute intake findings
Biological markers, including serum or plasma osmolality, and to some extent urine osmolality, are additional markers of hydration status
[10, 33, 34]. Until recently, hydration biomarkers were not included in NHANES data. In the 2009–2010 cycle, urine osmolality data were collected. Upon release of additional cycles that collect this data (to increase the sample size and availability of samples taken early in the morning), future work could examine patterns of this variable by population sub-group. However, no established cutoffs for hydration adequacy based on urine osmolality have been established at the population level.
The present analyses of the observed water intakes relative to the indices of hydration suggest that water consumption ought to be monitored more closely
. In 2010, EFSA published a 48-page report on water consumption, arguing that water is often disregarded in national and international recommendations or is very cursorily treated
. For example, the 2010 US Dietary Guidelines Advisory Group report devoted only two pages to water, stating that most healthy people consumed adequate water to meet their needs. Because water needs vary considerably, they concluded that a minimum intake of water could not be set
The current study was unique in focusing on the consumption of plain drinking water and other beverages using the most recently available data for American adults. Previous work evaluating beverage intakes of adults has focused on the predictors and correlates of consuming specific beverages
[37–40], the relation between beverage intake and measures of diet quality
[13, 15, 40], the contribution of beverages to nutrient or energy intake
[41, 42], or time-trends in beverage consumption patterns or preferences
[43, 44]. One important finding from the current study was differences in tap vs. bottled water consumption by socio-demographic factors, namely race/ethnicity, but also by family income. A recent study focused on the relation between the perceived safety of tap water and the intake of sugar sweetened beverages among US adults, nothing that those who viewed tap water as safe to drink tended to be older, have higher incomes, be better educated, were more active and were more likely to be white
. Water safety has previously been raised as a concern and may explain the higher proportion of Mexican-American and other Hispanics who consume bottled vs. tap water
[46, 47]. However, none of these studies measured water consumption directly. It is unclear why a weaker preference was observed for the non-Hispanic black population in the present study.
Another recent report, based on the 2007 National Cancer Institute’s Food Attitudes and Behaviors Survey, examined behaviors and attitudes associated with low consumption of plain water among US adults
. Here, the adjusted odds of drinking <4 cups of water per day was associated with older age (>55y), sedentary lifestyles and low consumption of fruits and vegetables, but not with education or incomes. However, in this study regular water consumption was reported via questionnaire, not by measurement in a dietary recall or interview.
The present study therefore fills a gap in the existing knowledge regarding water consumption patterns among US adults. Although older adults are known to represent a group at risk, current data on water consumption patterns have not been available previously.
Future guidelines on beverage consumption should take plain drinking water into account. This is particularly important given the size of the shortfall between observed intakes and IOM AI values for older adults. This is particularly important given the increased likelihood of having an impaired thirst mechanism among older adults
Total water intake can be increased in a number of ways. The most effective way would be to increase the consumption of plain water, including either tap or bottled water. Promoting water intake is currently highlighted in the 2010 Dietary Guidelines for Americans as a potential replacement for sugar-sweetened beverages
. Future dietary surveillance should monitor total water intake to determine if reducing intake of sugar-sweetened beverages has a negative impact on total water intake.
In the present analyses of NHANES 2005–2010 data, non-beverage food sources accounted for 17-25% of total dietary water, as compared to 19% reported in the 2010 Dietary Guidelines for Americans Advisory Committee report
, though methods for assessing water intake have changed from previous NHANES cycles. This observation highlights that increasing consumption of low energy density foods with high water content foods (e.g., fruits/vegetables) is another approach to increase water intakes, while subsequently improving overall diet quality.
The present analyses had some limitations. First, the NHANES data are based on self-report and are subject to random and systematic reporting errors. Each of the two dietary recall days used different methods to collect the data, which 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 probable that many respondents under-reported water intakes due to drinking water lacking salience. This may be particularly problematic for events where little water was consumed or it was consumed casually (e.g., repeatedly being refilled at a restaurant). It is important to note that these data cannot be directly compared to those from pervious cycles of NHANES (prior to 2005), as the mode for collecting data on water intake changed. In previous cycles of NHANES water intake was measured at the end of the recall via questionnaire, whereas in more recent cycles, water is measured as part of the 24-hour recall. Comparisons of water intake for the entire population and population sub-groups between 1999–2004 and 2005–2006 reveal that estimated water intakes are approximately 15% lower using newer as compared to older data
. While this difference may be attributable to secular changes in water intake, they are more likely driven by changes in data collection. Caution should be applied when comparing the results presented here to data collected prior to 2005. An additional limitation in evaluating adequacy of water intake at the population-level is the lack of Recommended Daily Allowance values for water. While the AI values established by the IOM provide some benchmark in evaluating water intake, the proportions above/below this value should be interpreted cautiously. The 2010 Dietary Guidelines for Americans contends that the combination of thirst and normal eating/drinking behaviors provides sufficient water
. Surveillance of water intake from dietary data should be carefully monitored and the use of biomarkers to evaluate hydration status at the population-level should be a priority.
Nonetheless, the present analyses represent one of the few explorations of the consumption of water in the US and can be used to inform approaches to improving the overall diet quality and hydration status of the population. Advantages of the data used here include the use of a large and nationally representative dataset that forms the basis for dietary surveillance in the US.