GONZALES, Tex. — In a dusty lot off the main highway in this South Texas town, Vern Sartin pointed to a collection of hose hookups and large storage tanks used for collecting wastewater from hydraulic fracturing jobs.

“We run about 30 to 40 trucks a day, 24-7,” Mr. Sartin said. “Depending on how the oil fracking is going out there, if they’re hustling and bustling, then we’re hustling and bustling.”

Mr. Sartin is a watchman at a disposal well operated by Gulf Coast Acquisitions, where each day oil and gas companies dispose of wastewater by pumping it deep underground.

Wastewater disposal wells like this one are becoming a common landmark in the drilling regions of Texas as the water-intensive practice of hydraulic fracturing, or fracking, continues to spread. In the fracking process, several million gallons of water, combined with sand and chemicals, are sent down a well to break up rock and retrieve oil and gas. Some of the fluid comes back up, along with additional underground water.