Natural gas has been touted by some as a key “bridge fuel” that will transition the United States toward a more low-carbon energy economy. Energy analysts, including the United States Energy Information Administration (U.S. EIA), project that the United States will become increasingly reliant on natural gas. According to U.S. EIA estimates released in January 2012, natural gas production is projected to increase by nearly 30% over the next 25 years, from 22 trillion cubic feet in 2010 to 28 trillion cubic feet in 2035.1 The growth in natural gas production is driven by a dramatic increase in domestic shale gas production, and by 2021, the United States is projected to be a net exporter of natural gas.

Although extracting natural gas from unconventional sources is more complex and costly than conventional natural gas recovery, technological improvements have made extraction from unconventional sources more economically viable in recent years. In particular, the combination of horizontal drilling and hydraulic fracturing has greatly increased the productivity of natural gas wells. These new techniques, however, have raised concerns about the adverse environmental and social impacts of these practices, especially related to impacts on water resources.