I am curious about how everyone uses their sensor and swimming, a hot tub, or other water activities. I just tried putting my receiver in Ziploc sandwich bag and then inside a larger Ziploc bag. It worked keeping the receiver dry but I needed use a safety pin to close my swimming suit pocket so the receiver wouldn't float away.
I know I can shutdown the receiver but it seems easier to try to keep it going.
I try to always keep mine going too, unless I am going to be far away from the receiver for an extended period of time. I take showers and my sensor is OK for two weeks. My sensors maintain good accuracy for two weeks. I have all 4 sides of the sensor taped down, but I do not put any tape on the transmitter. Th water from the shower does not affect the sensor. Immersing the sensor in water while swimming is probably safe too, but I have not done that. You could call Dexcom to find out.
You can wear the sensors in water no problem. The major problem that people find is that the adhesive starts to break down prematurely.
My absolutely favorite way of preserving the adhesive (all of the time) is using the STS shower covers. You can buy them in packs of 10. They came with the original, non-waterproof systems and create a watertight barrier around the sensor. This really prolongs the adhesive life and is easy to change once the shower cover adhesive wears off (5-6 days).
As for swimming with the receiver -- BE CAREFUL! If you get the receiver wet, Dexcom will not replace it free of charge anymore. I'm not sure what they charge for a replacement but I'm not sure if its worth it. It also causes one to be cautious in the bathroom as I know many who inadvertently drop it in the toilet (still not covered)!
I've always used swimming as a great opportunity to charge my receiver at home.