The Texas Water Development Board estimates that up to 1.5 million water wells have been drilled in the state since 1900, although up to 500,000 of these may now be abandoned.

Hiring a driller these days is not cheap. A new residential well costs $12,000 to $30,000, Mr. Blair said, with the difference due to variables like how deep the well goes and the size of the pump. The well drilled in Spicewood took a day.

But lots of Texans want one, and the wait can be frustrating. G. W. Franzen, a Matagorda County rice farmer, plans to drill two test wells on his land to see if enough groundwater exists to replace some surface water, which he fears losing access to because of emergency measures by the Lower Colorado River Authority. But he cannot get a driller until May or June.

“That’s not soon enough for the 2012 crop,” he said.

Larry Schwope, a co-owner of H. W. Schwope & Sons, a drilling company in the Hill Country town of Boerne, said his company had seen a crush of business because of the drought. And barring some “real good rains” soon, demand could pick up further this summer, he said.

A number of regulators around the state, eager to preserve groundwater supplies, have been recently tightening restrictions on how much individuals can withdraw. Such changes, along with the drought, have made the groundwater supply business somewhat busier, according to Kevin Spencer, president of R. W. Harden & Associates, an Austin-based hydrology firm. His firm procures companies to drill large wells that serve cities like Groesbeck, and he said he had not had trouble finding drillers for municipal wells despite the drought and the backlog for smaller drillers.

Mr. Blair fears that in the future, the Legislature could alter groundwater rules in parts of Travis County to bar people who are on city water from drilling a well.

Meanwhile, despite the booming demand for water wells, some drillers are drifting toward a more lucrative business — oil and gas. Mr. Blair, of Bee Cave Drilling, said that several major water well companies in Central and North Texas had switched to drilling for fossil fuels, lured by the prospect of making twice as much money.

Mr. Blair, however, is sticking to water, which is less boom-and-bust-prone than oil and gas.

“I like water because it’s very steady,” Mr. Blair said. “People always need water.”