Outdated rules governing drinking water leave the U.S. population at risk to exposure to harmful fracking chemicals, an advocacy group said.

The Government Accountability Office, the congressional watchdog, found the Environmental Protection Agency lacks the resources needed to effectively monitor water contamination and the seismic activity associated with hydraulic fracturing, known also as fracking. GAO added that EPA's authority was hindered by outdated measures.

Amy Mall, a policy analyst at the Natural Resources Defense Council, said the GAO report reinforces some of the fears associated with fracking.

"From drinking water contamination to man-made earthquakes, the reckless way oil and gas companies deal with their waste is a big problem," she said in a statement Monday. "EPA needs to rein in this industry run amok."

Fracking involves the injection of large amounts of water and sand mixed with a trace amount of chemicals that some critics consider harmful. A series of tremors, most recently in Oklahoma, were associated with the drilling practice behind the glut of oil and natural gas in the United States.

GAO said it was concerned about the safety of the nation's drinking water.