Via Popular Science:
Still, drinking your urine has no known health benefit. Urine is at least 95 percent water, but the remaining 5 percent is not very good for you—that’s why your body is getting rid of it. It carries excess electrolytes, such as chloride, sodium and potassium (urine also carries small traces of excess toxins in the form of acids from your kidney, but you’d need to drink a lot for that to do damage). Electrolytes enable some of our cells to conduct electricity, but too much sodium draws water out of our cells, dehydrating us, and too much potassium leads to a heart attack. “Think about it like drinking ocean water,” says Jeff Giullian, a nephrologist (kidney doctor) at South Denver Nephrology Associates in Colorado. “It’s going to dehydrate you and do significantly more harm than good.”
Dan Woolley would disagree. He spent 65 hours trapped beneath the rubble of the Hotel Montana in Haiti after last year’s earthquake and partially attributes his survival to drinking his own urine—many survivors do. Yet survival experts are split on the issue. Bear Grylls, the host of the TV show Man vs. Wild, is for it (Woolley credits Grylls for teaching him the trick), but the star ofSurvivorman, Les Stroud, is not. The U.S. Army Survival Handbook lists urine on its “do not drink” list, but Aron Ralston, the adventurer pinned under a boulder and forced to sever his own arm, drank his urine too (both acts were depicted in the movie 127 Hours).
Drinking urine for survival is even more harmful, since dehydration makes it less dilute and all those electrolytes and acids appear in greater concentration, making a bad situation worse. Also, it’s gross.