FIGURE 4-17 Daily fluid (water) requirements as related to air temperature and activity from studies conducted by the U.S. Army and used previously to estimate water requirements (1959). Top line (a) represents “hard work” in sun for 8 h/ day. Second line (b) represents moderate work in sun for 8 h/day. The bottom line (c) represents resting in shade for 8 h/day.

requirements range in sedentary, active, and very active persons from 3 to 6 L/day in temperate climates and from 4 to 12 L/day in hot climates (Brown, 1947b; Lee, 1964; Sawka and Montain, 2001; U.S. Army, 1959).

Fluid requirement data, based on intake, was reported in 1947 for soldiers working in different climates (Brown, 1947b). Figure 4-16 provides their reported relationships between daily maximal and mean air temperature values at two levels of physical activity on daily fluid requirements (qt/day, 1 qt = 0.95 L). This analysis did not specify the exact metabolic rates (kcal/day) or climatic heat stress encountered (e.g., radiant heat, humidity, air motion), and the experiments were mostly conducted in desert climates. Note that if the daily mean temperature was 30°C (86°F), the daily fluid requirements approximated ≈ 10 qt (9.5 L) if working 8 hours per day or ≈ 5 qt (4.5 L) if resting in the shade. Figure 4-16 suggests that in extreme heat stress and activity conditions, the daily fluid requirements could be greater than 16 qt (15.2 L). However, most persons reduce their activity level in hot weather, so such high daily fluid requirements would be for very physically fit, heat acclima-