A new regional effort is underway to answer a question that affects everyone in the D.C. area: What happens if the Potomac River can’t be used for drinking water?
The area’s three water companies — WSSC Water, the Washington Aqueduct and Fairfax Water — are launching a $25 million, two‑year study called “Secure the Source,” which is aimed at identifying a large-scale backup water supply for the region.
“The entire Washington metropolitan region — that’s over 5 million people — we rely primarily on a single source, and that’s the Potomac River for drinking water,” said Dr. Priscilla To, WSSC Water’s director of operational reliability and resilience.
That reliance on a single source across D.C., Maryland and Northern Virginia has long been recognized as a vulnerability, particularly given recent infrastructure concerns and a major sewage spill earlier this year that highlighted the system’s fragility.
This study will pick up where a previous U.S. Army Corps of Engineers $3 million study left off and will be paid for by the region’s water suppliers.
“We are currently still working out the details of that cost-sharing agreement, but at the same time, even as we look for other sources of funding for the study, we are also recognizing that it’s very important to have regional support for the funding of an eventual solution, which will be a much bigger investment,” To said.
A water system designed for the entire DC region
Currently, the D.C. region has limited backup capacity — in some cases just about a day’s worth of water if the Potomac River were suddenly unavailable — underscoring the importance of long-term planning.
“As the regional water suppliers, we recognize that there’s a need to pursue large-scale solutions — ones that would provide emergency water backup for several weeks for the entire region,” To said.
A key goal of the study is ensuring any new solution works across jurisdictional lines.
That includes developing an infrastructure that would allow WSSC Water, the Washington Aqueduct and Fairfax Water to have access to the regional second source or storage, in an emergency.
“We are looking at how our water supply system could provide more resilience to every system in D.C., in Maryland and in Virginia — and that would include looking at interconnections,” To said.
Earlier this year, the Army Corps of Engineers completed a study focused on near-term improvements, including expanding storage at the Dalecarlia Reservoir, which supplies the Washington Aqueduct system. But officials acknowledged that expanding that reservoir would only provide limited additional storage — measured in hours, not weeks — and wouldn’t solve the region’s long-term need for a true backup source
This new regional study will focus on options capable of sustaining the entire metropolitan area for an extended period of time if the Potomac River becomes unusable because of drought or contamination.
For now, water continues to flow safely from the Potomac. But regional leaders say planning for the unexpected is critical — especially when so many people depend on a single river.
“We’re looking at rock quarries in both Maryland and Virginia that would serve as storage for water in emergencies,” To said, including “the option of using wastewater and treating it to a higher standard for reuse.”
To said once the large-scale options are evaluated, the water companies will carry forward the best option and begin the design process.
Michael Nardolilli, executive director of the Interstate Commission on the Potomac River Basin agreed.
“This study is about ensuring that future generations inherit a water system that is resilient, reliable and prepared for the challenges ahead,” Nardolilli said.
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