the AI for men 19 to 30 years of age is set at 3.7 L/day of total water (from foods and fluids), while for women in the same age group, the AI is set at 2.7 L/day. In dietary survey data (Appendix Tables D-3 and F-1), water from food provided 19 percent of total water intake, or 0.7 L/day for men and 0.5 L/day for women in the United States (Appendix Table D-4). Fluids (drinking water and beverages) consumed were 3.0 L (about 12 cups)/day and 2.2 L (91/4 cups)/day for 19- to 30-year-old men and women, respectively, which represented about 81 percent of total water intake (Appendix Table D-3). Individuals who meet the recommended 60 minutes per day of moderate physical activity (IOM, 2002/2005) can easily meet the AI for total water through drinking water, beverages, and food (see Table 4-15).
A number of foods (especially fruits and vegetables) contain a substantial amount of water (moisture) (see Table 4-14). Unlike most other nutrients, intake of water is driven by need, as well as other factors. Because excessive water consumption does not occur in healthy people, no Tolerable Upper Intake Level (UL) was set. It is possible to meet the AI for total water by consuming little or no plain water, but instead by consuming a mixed diet (including fruits and vegetables, most of which are over 90 percent water by weight; meat, fish, and poultry, which contain about 60 to 70 percent water by weight; and other beverages, such as fruit juices and milk [see Table 4-14]).
As discussed in Chapter 4, it is important to note that water requirements cannot be considered in isolation from macronutrient and electrolyte consumption because these nutrients are critical to water balance. In addition, an individual’s water requirement can vary extensively due to physical activity levels and exposure to varied environments. The majority of body water is associated with fat-free mass (70 to 75 percent) in adults. Total body water averages approximately 60 percent of body weight with a range of 45 to 75 percent due primarily to differences in body composition. Total body water deficits of as little as 2 percent of body weight (e.g., a loss of 1.4 kg [about 1.4 L] in a 70-kg adult) can significantly impair both cognitive function and motor control.
Diet composition, physical activity level, environmental exposure, pathophysiological factors (e.g., diabetes mellitus, cystic fibrosis, renal disease), and use of diuretics or other medications all impact water needs, which vary daily.
The increase in solute loads of various beverages (e.g., milk or sports drinks) are minimal in terms of need to adjust the volume to correct for additional excretory load. Ingestion of fluids containing