Well, you're a gutsy little thing to try your maiden backpacking voyage in the Tx summer.
Just tell yourself before you even embark that if things don't work out as you had hoped, then you'll give it another try under better climate conditions.
Stash a few gallons in your car just in case. And, yes, you can boil water to purify. Let it go a good two minutes at a rolling boil. You could also use iodine or chlorine dioxide tablets for purification. Bring a handerkerchief or bandanna to filter any large particles, silt or sediment.
Congratulations and welcome to the wonderful world of backpacking. You're gonna love it.
(Well, maybe your first trip won't be the best....mine wasn't.....but you'll learn a lot.)