Hello from WDW! I'm sitting in the Wonderland Cafe of Disney Quest as I type this! We just finished a day at Typhoon Lagoon and the kids are still going strong but DH is dozing away in the seat opposite me!
To answer your question: If you have an AP, you can get $3 off of the gate price of adult admission for yourself and up to 3 other people. Other than that, I don't think there are any discounts. You might want to consider purchasing MYW passes with the Magic Plus option instead. The pluses can be used for waterpark admission.