As I remember the training I received (many years ago), urine was only considered as a possible method to clean a wound in a situation where medieval was not an option and you had to provide long term care. It was never considered sterile (probably a more recently developed myth) and only a last resort for cleaning dirt and debris out of a wound. We were told to use the person's own urine, and to further cleanse the wound with alcohol or peroxide if it was available. Clean water was always a first choice, and taking the time to boil the water, or purify it in any other way, was worth the time and effort as the dirt and debris will take time to begin an infection. Of course there are many variables involved in this. The dirt and debris need to be removed before the wound is bandaged up for long term care. Understand that this scenario was taught at military survival schools for a long term evasion or isolation situation only. It also did not receive more than a brief mention as a possible alternative to flushing the wound with clean water, it was never considered a primary method of cleaning a wound.