In desert survival scenarios people often make the mistake of thinking they’re not sweating because their skin is not wet. What is happening is that the sweat is evaporating quicker than it can collect on the skin’s surface. If you rest your hand on your skin for a few moments you will find it dripping with sweat.
A lot of water is lost through sweating just sitting in one place doing nothing. Up to two and a half quarts of water every day. In extreme hot weather it’s possible to lose a gallon of water per hour in sweat. Cody Lundin author of, “What To do When All Hell Breaks Loose”, recommends three gallons of water per person per day. If extreme activity is going to be taking place then he advises even more.
The need to transport that much water per person per day in hot climates necessitates that one gets themselves in as good as shape as possible for the strain of carrying several gallons of water long distances.