Now we just flush it away, but historically, pee had real value. The Smithsonian lists some of the things that it used to be used for:
1) Tanning leather. Urine is full of urea, which degrades into ammonia.
Ammonia in water acts as a caustic but weak base. Its high pH breaks down organic material, making urine the perfect substance for ancients to use in softening and tanning animal hides. Soaking animal skins in urine also made it easier for leather workers to remove hair and bits of flesh from the skin.
2) Cleaning and whitening clothes. The ammonia removes stains and intensifies the colors of dyes. "Many launderers preferred it to soap."
3) Gunpowder. Urine can be used to make saltpetre, a key ingredient of the explosive.
4) Tooth Whitener. Again, from the ammonia.
5) Commenters picked up the subject and noted that urine was also used as a health supplement (Gandhi would drink his own every morning and Madonna has claimed that she used it to cure her athlete's foot)
6) Today one of the most important uses of urine would be to recover the phosphorus. We explained how to do that here. Really, given how valuable the stuff is, perhaps it is time to stop throwing it away.
Via Fast Company