Since they spend plenty of time underground to escape the daytime heat, their burrows become quite humid. When gathering seeds, rather than eating them immediately, they store them in the burrows, which allows the seeds to reabsorb the moisture in the air. The Kangaroo Rat then regains this water when they consume the seeds.
Probably the most important adaptation is the animal's efficient kidneys. Due to the rodent's lengthened loop of Henle they can produce urine which is 5 times more concentrated than maximally concentrated human urine. Because of this ability, these Kangaroo Rats never actually have to drink. The water produced within its cells during oxidation of food is sufficient for their body. Furthermore, its nasal passages can reabsorb water vapor from its own breath. To top it off, Kangaroo Rats have no sweat glands, so they can't lose water by perspiring. With all of that figured out, these little guys can focus their attention on avoiding snakes.