[cazum]

I think this should go without saying, but this is obviously untrue. Yet, I've heard it more times than I could ever recall.

Where did this myth come from?

[dragonwriter]

It came from the time when harmless bacteria weren't recognized as a thing, only infectious germs; urine from a healthy person does not tend to contain harmful bacteria and is this not an infection vector, thus it was held, incorrectly, to be sterile.