Tom Kenworthy: Fracking can strain U.S. water supplies

  As the level of hydraulic fracturing of oil and gas wells in the United States has intensified in recent years, much of the mounting public concern has centered on fears that underground water supplies could be contaminated with the toxic chemicals used in the well-stimulation technique that cracks rock formations and releases trapped oil and gas. But in some parts of the country, worries are also growing about fracking’s effect on the water supply, as the water-intensive process stirs competition for the resources already stretched thin by drought or other factors.