There was a study done about water entering the vagina because there were so many people up in arms about water births being linked to infections after the bag of waters was broken. It was a big study, and I can't point anyone towards a specific link. Essentially (and I am trying to remember details but I just don't have many) they gave women tampons that were treated, or the water that they had them immerse themselves in was treated....something like that, and then they inspected the tampons....gosh this is terrible. Regardless, they were able to prove that water didn't enter the vaginal canal to any noticeable degree whatsoever. Hence the reason that it's actually quite quite safe to be in a birthing tub even after your water has broken.