Starvation and Thirst
Sometimes heroes might find themselves without food and water. In normal climates, heroes need at least 1/2 gallon of fluids and about 1/4 pound of decent food per day to avoid the threat of starvation. In very hot climates, heroes need two or three times as much water to avoid dehydration.
A character can go without water for one day plus a number of hours equal to his or her Constitution score. After this, the character must make a Constitution check each hour (DC 10, +1 for each previous check) or take 1d6 points of damage.
A character can go without food for three days, in growing discomfort. After this, the character must make a Constitution check each day (DC 10, +1 for each previous check) or sustain 1d6 points of damage.
Damage from thirst or starvation cannot be recovered until the hero gets water or food, as needed. Even magical or psionic effects that restore hit points cannot heal this damage.