No fish for Greyson

We've had Greyson for almost two years now, and we've also had our beta fish for about the same amount of time. As you can see from the picture below, Greyson loves to drink the water out of the fish bowl.  He doesn't want the fish.  He hasn't ever even tried to get it, although he does sit and watch it swim around after he's finished drinking. The odd thing about it is that this is the ONLY water that Grey will drink.  He always has fresh water near his food, and Anah has her bowl of fresh water that Grey could drink from, but he doesn't.  Never has.  This is the only water he will touch.  So I just have to make sure that I keep the fish bowl filled with water on a regular basis.