We had this same problem with my daughter last summer. Katie is not a child who is known to be able to hold her pee, usually she goes to the bathroom every hour and a half or so. We use to go to the pool at least 3 times a week and when we were there she wouldn't use the bathroom at all. I would often times ask her if she had to go to the bathroom and she would say no, I got a little curious about if she was peeing in the pool or if she just didn't have to go. I decided to figure it out. I followed her into the bathroom at the pool while we were getting ready to go swimming, I made sure that she went pee, I said, "If you don't go pee in the toilet now, you will not be going swimming." I did this so that I knew that she went and she wouldn't go pee so much in the pool. She went and we went swimming. I am always with my children in the pool (my youngest is 3 and needs me to hold him, he wears a diaper in the water) so I was playing with them one day and I reminded her that she needed to go to the toilet and pee if she needed to go because it wasn't sanitary to go pee in the pool, others have to swim in your pee if you do. She said she didn't and I said ok (I knew she did because she was "holding" herself). I was playing with her and all of a sudden I felt a surge of warm water near me. I knew she had just peed in the pool. I was furious and I told her to get out of the pool. I took her over to where we were sitting and I lectured her about how you do not pee in the pool, I told her that it was the last time she would pee in the pool and that the next week she was going to be wearing a diaper. I also told her that when she was at home, because peeing in the pool is not going pee in the toilet I thought of it as an accident and that she would be wearing a diaper for the rest of the day (I have to say, she wets the bed every night, so we have diapers). She was mad and started to pout, I told her that she made the decision and was the way it would be and if she wanted to pout we would go home. She sat there and pouted so we all went home, her sibilings were very angry with her and they let her know it all the way home. When we got home she was diapered and spanked (because she said some things in the car that got her in trouble and she was not being good at the pool and acting like a brat by pouting). When her dad came home from work, I took her siblings to the pool so that they could get their swim time in. I recommend that you do this to your daughter. My daughter learned her lesson quickly and I am glad that I did it. She wore diapers to the pool for about 5 trips.