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Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate
from approximately 0.7 L/hour in temperate weather to approximately 1.1 L/hour in warm weather when performing the same event (Cheuvront et al., 2002). Clearly these exertional rates cannot be sustained for 24 hours. The effect of sustaining these high sweating rates can markedly increase daily total water requirements. For example, the daily fluid intake of soldiers performing either “normal” work (~ 3,350 kcal/day) or physical training (~ 5,500 kcal/day) over a 12-day period in hot climate (mean daytime conditions 40°C [104°F] and 29 percent relative humidity) averaged approximately 7 and 11 L/day for the “normal” and physical training groups, respectively (Mudambo et al., 1997b).
Several analyses have attempted to quantify the effects of hot weather on increasing daily fluid (total water) requirements (Brown, 1947b; Lee, 1964; Sawka and Montain, 2001; U.S. Army, 1959). These analyses (Figures 4-16, 4-17, and 4-18) suggest that daily fluid
FIGURE 4-16 Daily fluid (water) requirements in soldiers as related to air temperature and activity from studies conducted by Brown (1947b). Top line represents “hard work” 8 h/day. Second line represents the same work but performed at night. Third line represents resting in shade. Bottom line represents the amount of water saved by working at night. Reprinted with permission from the Papers of Edward Adolph collection at the Edward G. Miner Library, University of Rochester Medical Center.