I noticed a complete lack of water park ads this time around -- didn't see a single one on a bus during my whole visit. But as you say, they didn't even advertise specific parks or features, just "hey! water parks are a fun thing!"Even the bus advertisements are generic and do nothing more than say "hey these things exist".
My friends and I always make one day mid-week for a water park; it's a great way to relax after a few days of doing the main parks full-bore.