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Potomac River Cooperative System

During times of drought, natural flows on the Potomac may not always be sufficient to allow water withdrawals by the utilities while still maintaining a minimum flow in the river for sustaining aquatic resources. In such cases, a cooperative entity staffed by the Interstate Commission on the Potomac River Basin manages the water system as a whole. This group is known as the Section for Cooperative Water Supply Operations on the Potomac (CO-OP), and is formally associated with the three major supply agencies by the Water Supply Coordination Agreement of 1982. (See Regional Agreements)

The three major supply agencies have paid for water storage held in two reservoirs in the Potomac Basin, which can augment water supply during low flow conditions so that the region's water supply demands can be met without violating recommended environmental flow-by. Jennings Randolph Reservoir in the upper reaches of the Potomac River Basin stores 13 billion gallons of water that may be allocated to water supply augmentation, but water released from the reservoir must travel for 7-9 days before reaching the Washington metropolitan region. Located in Montgomery County, Little Seneca Reservoir has 4 billion gallons of storage, which can quickly augment flow in stretches of the Potomac where the intakes for the major supply agencies are located.

Go to ICPRB's website for more information on how CO-OP manages regional water supply coordination.

The Washington metropolitan region gets nearly 90% of its drinking water from the Potomac River. Its supply is further augmented by water from the Jennings Randolph and Little Seneca Reservoirs, the Patuxent and Occoquan rivers, Goose Creek (a Potomac Tributary), Lake Manassas (which feeds the Occoquan), and groundwater resources.

Three major water supply agencies furnish about 95% of the metropolitan region's water. These are the Washington Aqueduct Division of the U.S. Army Corps of Engineers (WAD), the Fairfax County Water Authority (FCWA) and the Washington Suburban Sanitary Commission (WSSC). A number of smaller agencies supply the remaining 5% of the water.

Some parts of the region get their water through distribution agencies, which purchase water wholesale from one or more water supply agencies.

See an interactive map of service areas, or click on the agencies or regions below to learn more about your own water supply.

Water Supply Agencies Fairfax Water Washington Aqueduct Division of the US Army Corps of Engineers (WAD) Washington Suburban Sanitary Commission (WSSC) City of Bowie Department of Public Works City of Fairfax Department of Utilities City of Frederick Department of Public Works Frederick County Division of Utilities and Solid Waste Management Town of Leesburg City of Manassas Department of Utilities City of Rockville Department of Public Works

Water Distribution Agencies Arlington County Department of Public Works District of Columbia Water and Sewer Authority City of Falls Church Department of Utilities City of Alexandria (Virginia-American Water Company) Loudoun County Sanitation Authority Prince William County Service Authority Town of Vienna Department of Public Works

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Water Suppliers or Water Distributors