The army puts pee on the "do not drink" list because of its salinity, where drinking urine will make you more dehydrated than if you drink nothing at all. However, the urine is sterile, does not have any bacterial (unless you have an infection), it contains electrolytes, some little bit of hormones, and mostly water!

The more hydrated you are, the more water (vs salt) there is in your pee. So, in extreme situation, if you know you are about to run out of water, you could save your pee and drink it early on, while the contents of your pee are still predominantly water.