The only other thing I can think of is that he feels more "secure" in the water bowl, & prefers it to his hides. What kind of hides does he have? He should at least have 2- one warm side & one cool side, but they also have to have the right dimensions for a snake to feel safe & like using them. They don't like high ceilings, more than one doorway, or large doorways, or "too much room"- they like to feel "snug"- that equals feeling "safe" to a snake.