If you are very concerned, it never hurts to pop into a vet and have a check-up and a fecal sample tested since this is a new snake to you. You can put in a smaller water bowl, not big enough to soak in, that way you can see if it is the water he is after or the comfort. If he tries to get himself in a smaller bowl then there may be an underlying reason he wants/needs to soak. I honestly think it is a security issue, he is comfortable in there. My bp will NOT use him warm hide if is over 90, so it stays 88-90, and my cool hide is about 80.
Don't worry too much!