It's funny you posted this message now...I just got back from my naturopath. I was seeing her about my 19-month old daughter, her immune system's been weakened from too many Antibiotics and recently she had a bad UTI with a temp. One of the things she gave me to help support her immune system (until she can get back in balance) is 500ppm Colloidal Silver . In addition to giving it orally, she said I could dab some on her "private" area once in a while to kill any e. coli on the outside.
But once someone has an UTI the bacteria has already travelled up the urinary tract and is inside the body. So bathing in it won't kill the bacteria inside the body.
I'm no expert but from what the naturopath said, the CS used on the skin would only be a preventative for further bacteria from going up the urinary tract.
Hope this helps!