Sorry to disagree Paul, but Disney Owl is indeed correct (I'm 99% certain anyway), it's free to park at water parks, Disney ones anyway, Wet and Wild charge the same set rate as the other Universal parks. I guess Disney expect most people to combine a water park day with a trip into a major park.
I'm a little surprised they've not started charging yet, it's not like Disney to give freebies! (I'm becoming a bit cynical nowadays!)
Ian