Well he could be soaking for a number of reasons...


-maybe he's getting ready to shed?
-Because he has mites (not saying he does but could be a possibility maybe?)
-to thermoregulate?
-maybe he feels secure in his small water dish?

Those are just a couple possibilities... with more information it would be easier to gauge why he might be in there... I've had some snakes that would just soak every once in a while... didn't have mites and the temps were dead on in their enclosure but they would occasionally take a dip and chill out every once and a while.