I rarely give up on Google. My search string would be:
campground water Dallas Texas
Here's my hit list: http://www.google.com/search?hl=en&q...r+Dallas+Texas
If I didn't find something in the first 3-4 pages, I would probably try contacting sporting goods stores in the area -- or any Chamber of Commerce office in the area.
You can also search on Texas tourism -- several good possibilities to give you the information you want.