For ambulatory activities, rates of sweating are nearly proportional to the two-thirds power of body weight. Therefore, a 91-kg man will sweat approximately 30% more than his 59-kg companion walking at the same speed.

Individuals exposed to hot environments generally drink insufficient fluids during physical activity to offset water lost from sweating. Heat acclimatization shortens the time delay between when sweating begins and when drinking is initiated. In addition, heat-acclimatized individuals drink more frequently and more closely match fluid intake with sweating rate; this results in less voluntary dehydration. During light exercise, heat-acclimatized soldiers can and often will drink sufficient quantities to sustain hydration. However, during moderate-to-heavy intensity exercise, drinking ad libitum generally replaces 50% to 70% of sweat losses,and deficits need to be addressed during rest breaks.

In hot, climatic extremes, daily water requirements for soldiers can range from 5 to 12 L/d. The Water Consumption Planning Factors study report (also known as the Potable Water Planning Guide), published by the US Army Combined Arms Support Command, recommends that each soldier be provided with 11.4 L of water per day (ie, intake for each soldier should be no more than 11.4 L of water per day).