The U.S. Environmental Protection Agency (EPA) is committed to identifying and responding to the challenges that a changing climate poses to human health and the environment. Scientific evidence demonstrates that the climate is changing at an increasingly rapid rate, outside the range to which society has adapted in the past. These changes can pose significant challenges to the EPA's ability to fulfill its mission. The EPA must adapt to climate change if it is to continue fulfilling its statutory, regulatory and programmatic requirements. The Agency is therefore anticipating and planning for future changes in climate to ensure it continues to fulfill its mission of protecting human health and the environment even as the climate changes. In February 2013, the EPA released its draft Climate Change Adaptation Plan to the public for review and comment. The plan relies on peer-reviewed scientific information and expert judgment to identify vulnerabilities to EPA's mission and goals from climate change. The plan also presents 10 priority actions that EPA will take to ensure that its programs, policies, rules, and operations will remain effective under future climatic conditions. The priority placed on mainstreaming climate adaptation within EPA complements efforts to encourage and mainstream adaptation planning across the entire federal government. This Implementation Plan provides an overview of the opportunities available to the Office of Water within the U.S. Environmental Protection Agency (EPA) to respond to the challenges that a changing climate poses for the successful operation of national programs to protect the quality of the national water resources and drinking water. This Plan is organized using the framework adopted by the EPA for each of its major national offices and regional offices. Key elements of the Plan address: Vulnerability of water resources, including clean water and drinking water programs, to climate change; Priority actions for water program response to climate change; Office of Water contribution to meeting EPA strategic measures on climate change; Legal and enforcement issues; Training and outreach for climate change adaptation; Partnerships with Tribes; Populations and places vulnerable to a changing climate; and Program evaluation and cross-Agency pilot projects.