This final report provides a review and synthesis of available scientific information concerning the relationship between hydraulic fracturing activities and drinking water resources in the United States. EPA found scientific evidence that hydraulic fracturing activities can impact drinking water resources under some circumstances. The report identifies certain conditions under which impacts from hydraulic fracturing activities can be more frequent or severe. EPA’s report advances the scientific understanding of hydraulic fracturing’s impact on drinking water resources, and can inform decisions by federal, state, tribal, and local officials; industry; and communities to protect drinking water resources now and in the future.