L/day (0.32 + 0.52). The AI is set at 0.8 L/day after rounding to the nearest 0.1 L. Based on CSFII, approximately 26 percent of total water intake is from foods, whereas 74 percent is from beverages (including formula and drinking water) for infants 7 to 12 months of age.

In general, the differences in body water content between children, adolescents, and adults are smaller than between infants and children. This is shown in Table 4-1 for total body water as a fraction of body mass (Altman, 1961). A gradual, modest decline during childhood and adolescence in total body water per fat-free mass and per body mass in shown in Figure 4-1 (Van Loan and Bolieau, 1996).

Based on water balance studies, daily water intake increases twofold between the first month of life and months 6 to 12 (Goellner et al., 1981). In contrast, the increase in the daily intake between the ages of 2 and 9 years is only about 5 to 10 percent (Table 4-4). Likewise, based on doubly labeled water measurements, daily water turnover per body mass declines rapidly between infancy and early childhood, but thereafter, the decline is modest.

There are a number of indicators that can be used for assessing water status; however, because of homeostatic responses, some degree of over- and underhydration can be compensated for over the short term. Therefore, there is not a single water intake level that can be recommended for ensuring adequate hydration and optimal health. Data from Third National Health and Nutrition Examination Survey (NHANES III) demonstrate that normal hydration status for children (12 to 18 years of age), as measured by serum osmo-