CARRIZO SPRINGS, Tex. — In this South Texas stretch of mesquite trees and cactus, where the land is sometimes too dry to grow crops, the local aquifer is being strained in the search for oil. The reason is hydraulic fracturing, or fracking, a drilling process that requires massive amounts of water.

“We just can’t sustain it,” Hugh Fitzsimons, a Dimmit County bison rancher who serves on the board of his local groundwater district, said last month as he drove his pickup down a dusty road.

From 2009 to 2012, water production from one well on his ranch fell by two-thirds, a problem Mr. Fitzsimons linked to nearby wells pumping water for fracking operations. A study commissioned by his groundwater district found that in a five-county area that includes Dimmit, fracking reduces the amount of water in the Carrizo-Wilcox Aquifer by the equivalent of one-third of the aquifer’s recharge. Recharge means the amount of water an aquifer regains from precipitation and other factors.

The amount of water used in hydraulic fracturing — roughly 4 million to 6 million gallons per oil or gas well — has stirred concerns around Texas as the drought wears on and the drilling boom continues.