Desert Dweller( Savage Species, p. 32)
You are adapted to a desert environment.
Desert terrain type,
As a desert dweller, you are more hardy than those who live in more gentle climates. Your Fortitude save DC to avoid subdual damage from heat is reduced to 10 (see Heat Dangers in Chapter 3 of the DUNGEON MASTER's Guide). In addition, you can go without water for a number of hours equal to 24 + twice your Constitution score (see Starvation and Thirst Dangers in Chapter 3 of the DUNGEON MASTER's Guide).