When you begin to deyhdrate, the first thing your body does is try to hold the liquid in. So dehydrated people do not pee.
Incidentally, that's why drunk people smell so bad - alcohol inhibits your kidneys, but your body still needs to get rid of its urea, so it eliminates a part of it through the sweat glands - yes, very drunk people literally begin to sweat urine.
I just think I'll go and have a shower now.
