1) ask the kids
2) you have been to the water parks so you and your kids know how much you liked them/fun you had
3) think July - hot, hot - nice break from the parks
If you asked me when my kids were young and home - I would say skip DHS. We all loved the water parks and we made it a point of going at least once for each trip. My kids are older and would still go but my two dil's don't like the chlorine/sharing/water/germ thing.
We just got back and my kids (4 and 6) surprisingly enjoyed DHS more than any other park because of all the Star Wars stuff. I would skip the water park.