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the minimal, average, and liberal water requirements approximated 2.1, 3.4, and 5.0 L/day, respectively. In addition, Adolph (1933) concluded that a convenient “liberal standard” for total water intake is 1 mL/kcal expended. Subsequent studies by Johnson (1964) recommended minimum daily water requirements of no less then 0.91 L for survival conditions and 3.0 L for hot weather.

Table 4-5 presents water balance studies that have estimated daily total water requirements for adults. These requirements are above minimal levels because some physical activity (although usually nominal) was allowed and because individuals self-selected the volume of consumed fluids (i.e., ad libitum water consumption). For the prolonged bed-rest studies, greater emphasis was placed on data obtained during the initial week, if available. Water balance studies suggest that the required water intake to maintain water balance for resting adult men is approximately 2.5 L/day (Adolph, 1933; Newburgh et al., 1930). If modest physical activity is performed, the

TABLE 4-5 Estimation of Daily Water Requirements of Adults from Water Balance Studies

Reference

Subjects

Conditions

Total Water Intake (L/d)

Women

 

Yokozawa et al., 1993

3 women

Temperate, bed-rest

≈ 1.6

Men

 

Newburgh et al., 1930

Repeated studies of men

Temperate, rest, variety of diets

≈ 2.6

Welch et al., 1958

53 men

Active, ambient temperature range of −30°C to +30°C

≈ 3.0 at −20°C to +20°C

≈ 6.0 at +30°C

Consolazio et al., 1967

6 men

Temperate, rest, starvation study

≈ 2.5 (1st 4 d; ~ 3.4 if corrected for negative balance)

Consolazio et al., 1968

24 men

Temperate, rest, sea level controls

≈ 2.5

Greenleaf et al., 1977

7 men

Temperate, bed-rest with 1 h of exercise/d

≈ 3.2

Gunga et al., 1993

6 men

Temperate, hyperbaric (1.5 atmospheres absolute), sedentary

≈ 3.2



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