If you're going to go to a water park go to the biggest one in the nation.
Schlitterbahn.
It's awesome.
64 acres of outdoor waterpark.
It has uphill water rides, pools for playing in, and I believe most of the rides are ridden in filtered Comal river water, so it should be relatively clean.
It is a water park resort, which means you can actually stay there, they allow food and drinks in the park, the food itself isn't expensive.
Plus it has the master blaster, "the best water ride in the nation."
<a target=new class=ftalternatingbarlinklarge href="http://www.schlitterbahn.com/">http://www.schlitterbahn.com/</a>