Water and Salt
Water is critical to the ability of plants and animals to acclimatize and survive in extreme environments, whether on the seas, in deserts, or in the high mountains. Dehydration is the most important cause of death from exposure to heat and may contribute to death during other types of extreme exposures. Lack of potable water is much more rapidly dangerous to human survival than lack of food. Furthermore, the popular notion that the human body acclimatizes to water deprivation is unfounded biologically. This misconception, or some twist on it, has caused the deaths of many a hardy but poorly informed explorer.
The misunderstanding about water stems from the fact that the human body adjusts to low water intake by conserving water. Although the body curtails its loss of water and salt in the first few days of exposure to hot climates, no scientific evidence has shown that minimum daily water requirements decrease with acclimatization. A hallmark of heat adaptation is actually an increase in the rate of water loss from sweating. Indeed, the old adage about conserving water by seeking shade in the day and walking only at night in the desert has much to recommend it. Nothing on Earth substitutes for potable water, and without an adequate supply death is inevitable. This chapter discusses how much water is enough under different conditions. It will become evident that obtaining an estimate of sufficient water is easier said than done, because requirements vary not just with environment, but also with behavior.