People who have had experience in field activities are probably deeply impressed by the dependence of outdoor sports on water. Adequate water supply is the most basic condition for ensuring outdoor living quality and physical health. Simply relying on mountains to eat mountains and relying on water to eat water can't make you solve thirst at any time, but it will consume more energy and bring health hazards. So in any book that introduces outdoor life, how to acquire, transport, preserve and rationally allocate and use limited drinking water is an important chapter. Because in many cases there is no water to drink is the key to the success or failure of an event.