It's certainly doable, but you'll be flat exhausted by the end. Remember, it's hot outside. Water slides and activities tend to use a lot of energy. Plus, both parks have stairs...lots and lots of stairs. We love the water parks and go often. However, we've never done both in the same day and rarely spend more than 4-5 hours at one. I'm a gym rat and quite well physically conditioned, and while I'm not wiped out after a day at a water park, I certainly know I've used energy. If I did both, I'd be exhausted by the end.
If you want to do it, I say go for it, but make sure you can sleep in the next day.