Well, I swim often and it has been a deterrent (one of many) from wearing my cgms as often as I would like. The transmitter can go in the water. The connection between the transmitter and the sensor is water tight. I've never disconnected the transmitter before swimming....seems that the water would not be kind to the sensor without the watertight seal of the transmitter.
The thing that is bothersome to me is that the pump loses signal after 1/2 hour and once you lose that connection, you have to recalibrate the pump at that time in order to get it going again. Calibration is better done far away (time wise) from boluses and eating, so it's hard for me to find a good time to do this during the day other than first thing in the morning.
Another thing I've noticed is that once I wear the transmitter/sensor in the pool or spa for any extended period of time, it loses it's accuracy from then on until I put a new one in.
All that said...nothing is impossible, and you will make it work if you want it to. Just trying to be honest about how it's gone down for me. I know others do this with very little problems.