There is no evidence to suggest that renal function and hydration status are different during lactation. Therefore, the AI for total water (drinking water, beverages, and food) is set based on median total water intakes during lactation estimated in the NHANES III (Appendix Table D-1). In this survey, water from food for this life stage group was estimated to provide 19 percent of total water intake (Appendix Table D-4).

Another approach to determining the total water needs during lactation would be to sum the nonpregnant AI (2.3, 2.7, and 2.9 L/ day for 14- through 18-, 19- through 30-, and 31- through 50-year-old females, respectively) and the water content of the average milk output during the first 6 months of lactation (0.78 L milk × 87 percent = 0.68 L water). This generates an estimated total water intake of 3.0, 3.4, and 3.6 L/day for lactating females 14 to 18, 19 to 30, and 31 to 50 years of age, respectively. These estimates closely coincide with the AI for total water based on median intake during lactation. Hence, the latter, median intake during lactation is used as the AI for all age groups.