Do you want to go to the pool?
Yes? Well, water you waiting for?
Do you want to go to the pool?
Yes? Well, water you waiting for?
Alright, listen up, smart guy. The joke is a pun. "Water" sounds like "what are." So, instead of asking what you are waiting for, it asks water you waiting for? Because, ya know, we're talking about a pool? You probably still don't get it because you're the kind of guy who wears socks with sandals.