An average-sized man requires two quarts of water a day. This requirement is doubled in both very dry conditions (such as the desert) or areas of high humidity (the jungle) as the character perspires constantly and begins to dehydrate.
If enough water isn't available, the hero begins to suffer from dehydration. Starting the first day after the water runs out, he must make a Vigor roll. Subtract 2 if the hero has less than half the required amount. Failure means the character gains a Fatigue level. After the first day, the character must make the required Vigor roll every 6 hours.
The Survival Skill: A successful Survival roll each day provides enough water (and food) for one person, or enough for five with a raise.
Savage Worlds Deluxe Edition p. 103