One of mine (Zara) likes to lick water off of surfaces. I think it just indicates they like their water that way. You might consider getting a CatIt water fountain. She might enjoy licking water off of the dome. I'm thinking about getting Zara one.
One of my mother's cats loves to lick dripping water off of human hands, so your cat is not unique.
On the advice side, I agree with mschauer; assuming you have water out at all times, your cat probably just likes water that way. A cat fountain might very well be a good way for him to get water off of a wet surface even when you aren't danging a wet hand.