Don't count on finding wood at the camp site. Many parks do not allow gathering of ground wood and even if they do, wood is often a scarce commodity in Texas. The best rule is to carry kindling, an adequate supply of firewood for small daily fires, and a fire container from home. Potable water is vital to the camper and trail rider. The best rule of thumb is to consider all streams contaminated for human drinking purposes.
Most parks have a source of safe water available to campers.
Whenever possible, use that water or bring water from home. The only really reliable purification process is boiling. Regardless, at sea level boil for at least three minutes and add one minute for every two thousand feet above sea level for relative safety. Prices vary as do purification methods. Spend some time checking these out before deciding which one to purchase.