So, your snake is spending lots and lots of time in its water. It isn't showing any signs of shedding and you're pretty sure it does not have mites. Why else would your snake spend lots of time in its water?
Are you sure there are no mites? Pop him in a white pillowcase overnight (advice by pythoninfinite) and see if you find any black specks on the pillowcase the next day. There are no black specks and nothing in the water when I soak him.
Does he have any retained skin on him that he is trying to get rid of? NO. Is your enclosure overheated? NO?
Check him thoroughly for ticks. Ticks can annoy them as much as mites can. I don't know that ticks are potentially dangerous to reptiles like they are to dogs and cats, but they are blood suckers and irritable. Your snake may be soaking, trying to relieve an irritation that you have not found. It pays to spend some closer attention to your snakes now and then, looking for raised scales, feeling for tiny bumps that shouldn't be there. Some ticks can be hard to see, and can be difficult to remove. As soon as you start harassing them the ticks may try to bury themselves deeper into the scales so have a pair of tweezers on hand so you can grasp those rotten suckers and get rid of them.
I've watched an intergrade of mine spend near two months in his water. I quarantined him, suspecting mites. Soaked him, sprayed him, fogged his tub and his enclosure. Are mites really that hard to see? They can be, especially on a dark snake but mites were not the problem. Today I took Jimmy out for some sunshine and after he warmed up I pulled him out to give him a really good close up going over. I was looking for mites, but pressing down on his skin as he slithered through my hands I felt some little bumps. The scales were raised at those bumps, and sure enough, tiny red looking ticks were there. I found three on him. He was very well behaved while I poked at him for so long but I couldn't feel or see anymore. So hopefully we found the reason why he was spending all his time in his water bowl. I never suspected ticks because he has not been anywhere to pick them up. So beats me how they found him, but they did.