DC Metro Water Supply Resilience

Interstate Commission on the Potomac River Basin

National Capital Region Water Supply Resilience

The Potomac River supplies 78% of the Washington, DC, metropolitan area’s water, with public water supply intakes located in the river just upstream of the city. During drought, water from three upstream reservoirs can be released if necessary to increase river flow. Public water suppliers in the region utilize the Potomac River as a source of raw water and distribute treated water to homes, businesses, and critical government facilities. Combined, they serve five million residents and over three million workers in the District and surrounding Maryland and Virginia jurisdictions. The region depends on water for use by residents and workers for drinking, cooking, bathing, and flushing toilets, use by hospitals and other medical facilities, fire suppression, and cooling water for industrial air conditioning systems.

Current threats to the region’s water supply include more severe droughts due to climate change and potential spills polluting the Potomac River.  The region’s water suppliers rely heavily on the Potomac River and would be faced with moderate to severe water shortages in the event of a loss of their Potomac supply.  A shutdown of Potomac River intakes is predicted to result in a critical loss of water in some areas of the region after just one day.

ICPRB’s 2017 study, Washington Metropolitan Area Water Supply Alternatives, evaluated a suite of options to address increased drought severity in the face of climate change and identified use of a local quarry to store an emergency backup supply of water as a recommended option. A subsequent ICPRB study, the Washington Metropolitan Area Water Supply Reliability Study: Demand and Resource Availability Forecast for the Year 2050 (2020), updated and refined the evaluation of benefits of additional supplemental storage. Another expert study, the National Capital Region Water Supply and Distribution System Redundancy Study, completed in 2016 for the Metropolitan Washington Council of Governments, concluded that raw water storage in a local quarry was an effective solution to the threat of water shortages. Other cities have also acquired quarries to increase resiliency. For example, Atlanta was formerly 100% dependent on the Chattahoochee River. As a solution, the city acquired the Bellwood Quarry Reservoir that increased its backup supply of water from 3 days to between 30 and 90 days.

In short, there are ways to increase the resiliency of the DC area’s water supply. An existing quarry, located in Montgomery County, Maryland, could potentially be converted to a regional raw water storage reservoir with tunnels to carry water by gravity to Washington metropolitan area treatment plants. The estimated project cost is $800 million. The time to start planning for such a facility is now.

The ICPRB is committed to continuing its role of assisting in the cooperative management of regional water resources and facilitating dialog between the multiple stakeholders where it has the authority, resources, and relevant expertise, in studying water resources problems, developing solutions, and sharing relevant information with policymakers and the public.