Water use for fracking by oil and gas operators in the Marcellus Shale region rose 20 percent between 2011 and 2016 as longer laterals were drilled to fracture more gas-bearing rock, even though the pace of well development slowed in response to low natural gas prices, a Duke University study said on Wednesday.

The rise was the smallest of any of the six U.S. regions studied, including the Permian Basin area of Texas, where water use surged by 770 percent over the period.

The study also said the volume of fracking waste water produced in the Marcellus – which includes Pennsylvania, West Virginia, eastern Ohio and southern New York, where fracking is banned — rose four-fold to 600,000 gallons in 2016, forcing energy companies to rely increasingly on holding the waste in underground injection wells. Read more.