[moultano]

Urine is sterile.

[niels_olson]

As a pathology resident, I assure you, the voided stream is not sterile, and definitely has all the building blocks necessary for bacterial growth.

That said, inland cities all recycle water. And they generally return water into the rivers that is cleaner than what they took out.

[Terr_]

Only before it starts leaving the body.