Water: do not ration water, ration sweat

The classic mistake is to save the water "for later" while you walk in the sun. FM 21-76 sums it up this way: conserve sweat, not water. The water in your canteen does not keep you alive; the water in your body does. Many people have been found dead from heat with water in their pack.

1. Drink when you are thirsty, and before you are if you are exerting yourself. Thirst arrives late: if you drink only because you are thirsty, you usually take in about two thirds of what you need.
2. Drink in frequent sips, not all at once. Most people cannot tolerate more than 1 liter at a time.
3. Reduce the loss, not the intake: stay in the shade, do not exert yourself during the hot hours, cover your skin, breathe through your nose, do not talk more than necessary.
4. Watch your urine. If it is scant and dark, you need more water. FM 21-76 says to produce at least half a liter of urine every 24 hours.
5. If you have very little water, do not "stretch" it in tiny sips while you walk in the sun: stop moving in the heat, find shade, and wait for night or rescue. Every hour still in the shade saves water you would use up walking.
6. Eat little if you have little water, and avoid salty foods, which increase thirst.

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