If the body didn't need it the first time around, why would it need it the second time around? Furthermore the kidneys flush out the bad stuff; they are cleaners much like the liver. Kidneys create urine by cleaning the toxins from the body. They clean the toxins via the bloodstream.
IMO, I don't need to drink my own waste to be healthy. I eat right, exercise, eat herbs, teas, liver cleanses, etc.