Urine contains waste products-urea, salt, ketones. The more concentrated, the more products per milliliter. probably not a good idea not to eat excreta (even if you can see the undigested kernels of corn, it is a bad idea) and analogously, unwise to drink urine, cuz it will recycle the waste products, Urine is sterile, unless something nasty is going on between bladder and the great outdoors. In WWI, soldiers in the trenches took turn urinating on each others hands to salvage the lost heat. One could pee into a solar still and collect condensate for drinking purposes. NASA has some technology for recycling waste-http://www.ctv.ca/servlet/ArticleNews/story/CTVNews/20071021/nasa_urine_071021/20071021?hub=TopStories.
Nasa apparently uses reverse osmosis, which is kinda tricky for survival kit use http://www.freedrinkingwater.com/infocenter.htm