Helenthereef

I agree with Richard, I have one who seems to thank she is an anaconda (she isn't) and will soak for 2 - 3 days every time after she has been fed. She's been doing it now for about 10 years, and has no other problems. The other 4, housed very close together, don't do it and all are healthy.

So, of course check up on the mites, the humidity, the temps, the hides, all the other things that have been suggested, but if all else is well, you might just have a water loving snake.