Adolph (1943) described the rates of water gain and water loss relative to different levels of water deficit and excess. Induced water deficits or water excesses resulted in compensatory changes in water gains and water losses until water balance was reestablished. Likewise, Newburgh and colleagues (1930) demonstrated the accuracy of water balance studies to be within 0.5 percent of the water volume. Therefore, ad libitum water balance studies can be used to estimate daily water requirements, provided the subjects have adequate time for rehydration and physiologic compensation (Adolph, 1943; Newburgh et al., 1930). In both these studies, total water intake was measured.

Table 4-4 presents water balance studies that have estimated daily total water requirements for infants and children. Note that daily total water requirements increase with age from early infancy (approximately 0.6 L) through childhood (approximately 1.7 L). Since infants have rapid growth, some investigators express the daily water needs relative to body mass.

The minimal daily water requirement depends upon the person’s diet, environment, and activity level. After reviewing early water balance studies, Adolph (1933) concluded that for most adult men,