Cover as much skin as possible, including your head, with clothing. Evaporation of sweat, which often causes the most significant water loss, occurs most rapidly on exposed skin.
Stay out of direct sunlight, and move as little as possible to reduce sweating. Walk at night, rest during the day.
Watch what you eat, since the digestive process uses water. If possible, stick to succulent fruits. Avoid salty foods, which increase thirst, and high-protein foods requiring water for digestion.
Breathe through your nose to reduce water loss from your mouth.
Move slowly, since you perspire more and expel more moisture with the heavy breathing that results from exertion.
Avoid alcohol, which dehydrates, and tobacco, which dries your airway.
Drink your water if you have just a little instead of rationing it. Best to ration your sweat, not your water.