SAN ANTONIO — In the heart of South Texas, where the muted grayish green of live oak and the slender leaves of the thorny mesquite dominate a landscape burdened by drought, hydraulic fracturing used more than 14 billion gallons of water last year.The number far outpaces estimates of what water use in the Eagle Ford Shale might have peaked at some time in the next decade and represents one more way in which the meteoric development of the oil field has blown past expectations.A widely cited study from the University of Texas at Austin, funded by the oil and gas industry, had predicted that hydraulic fracturing in the Eagle Ford would use a maximum of around 35,000 acre-feet of water annually. But the San Antonio Express-News looked at more than 23,000 Texas wells drilled from 2011 to 2013, including more than 6,100 in the Eagle Ford, and found that the oil field is already swallowing more water. Operators reported using around 43,770 acre-feet last year in 3,522 Eagle Ford wells, the approximate annual usage for 153,000 San Antonio households.“The oil and gas boom is requiring more water than we have,” said Hugh Fitzsimons, a Dimmit County rancher and a director of the Wintergarden Groundwater Conservation District. “Period.” Water always has been needed for oil and gas drilling, but not in this quantity. The combination of horizontal drilling with hydraulic fracturing has made it possible to drill in tight rock such as shale, which stores oil and gas but doesn’t let go of them easily. Hydraulic fracturing pumps a mix of water and chemicals at high pressure to break the shale. Then sand is added to the fluid in increasing amounts to hold open the fissures, letting oil and gas flow up the well to the surface. Cleaning and recycling water so it can be used in multiple wells is on the rise in the region, but it’s not standard practice. Some portion of those 14 billion Eagle Ford gallons used for fracturing — likely around 21 percent, according to the UT study — would have come from nonfreshwater sources: brackish aquifers that can’t be used for drinking, agriculture or livestock, or water that was recycled. Fracturing each Eagle Ford well took around 3.8 million gallons of water this year, down from 4 million gallons in 2012. But eight dozen wells used more than 10 million gallons of water — enough in each well to fill 15 Olympic-size swimming pools. The Express-News looked at data from the nonprofit Sky-Truth, which compiled reports from FracFocus, the national registry where oil and gas operators report the chemicals and water used in every well hydraulically fractured in the U.S.The data is not perfect. It’s likely incomplete, and there’s a lag between the time when a well is fractured and when the data gets reported. But it’s the best set of publicly available information about water use for hydraulic fracturing and gives some insight into the shale drilling boom. The UT paper said the Eagle Ford is a particularly difficult field to predict, and its lead author, Jean-Philippe Nicot, a research scientist at UT’s Bureau of Economic Geology, said he now thinks the actual use in the Eagle Ford is around 40,000 acre-feet annually. Karnes, La Salle and Gonzales counties in the Eagle Ford are the top crude oil producers in Texas. And the jobs and wealth added to the region have been unprecedented, even for a region already familiar with the boom-and-bust cycle of oil and gas. Private property rights, economics on an overwhelming magnitude, regulatory issues, drought and complex geological variation across a large aquifer are among the many issues tangled up in South Texas water use, along with the competition between agriculture, communities and industry. Geologist Darrell Brownlow, a resident of Wilson County who has a ranch in La Salle County with both oil and water wells, said there’s a trade-off at work.“There’s probably not a more complex situation,” Brownlow said. “It’s not something that’s easily solved. Ten years ago, you could have bought all the land you wanted in South Texas. It wasn’t worth anything.” Few made enough cattle ranching or through deer hunts to even pay property taxes. Now there’s less water, but much of the land can’t be bought at any price.