Army Corps Aims to Expand DC Reservoir to Improve Drinking Water Resilience

The expansion would provide an additional 12 hours of water storage, but officials say it's not a long-term fix for the region's water supply vulnerabilities.

Published on Mar. 2, 2026

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The U.S. Army Corps of Engineers is conducting a feasibility study to expand the Dalecarlia Reservoir in Washington, D.C. as a near-term solution to improve the region's drinking water resilience. While the expansion would only provide an additional 12 hours of water storage, officials say it's a necessary step to address the 'quite, quite dire' issues with the Potomac River being the sole source of drinking water for D.C., Arlington, and parts of Fairfax County. The Corps is also exploring longer-term regional solutions, such as using quarries in Maryland and Virginia, but says those options face significant logistical, real estate, and financial challenges.

Why it matters

The Potomac River is the sole source of drinking water for the D.C. region, leaving the area vulnerable to disruptions. Recent events, like the collapse of a portion of the Potomac Interceptor sewer line, have highlighted the need for more resilient water infrastructure and backup options. The reservoir expansion is an attempt to quickly address some of these near-term risks, while the Corps continues to study longer-term regional solutions.

The details

The proposed expansion of the Dalecarlia Reservoir would add approximately 70 million gallons per day of storage capacity, doubling the current capacity. This would provide an additional 12 hours of water storage, though it's unclear if that would be raw water from the Potomac or finished water after treatment. The expansion would not require acquiring any new land, as the land is already owned by the Washington Aqueduct. Other near-term options being considered include advanced water treatment technologies and water reuse. Longer-term regional solutions like using quarries in Maryland and Virginia face significant challenges and would take much more time to implement.

  • The U.S. Army Corps of Engineers has been conducting a three-year feasibility study funded by Congress and the Metropolitan Washington Council of Governments.
  • In November 2025, DC Water outlined plans to recycle water from its Blue Plains Advanced Wastewater Treatment Plant.
  • 10 years ago, in December 2016, WTOP first reported that the Travilah Quarry in Rockville, Maryland was being considered as an alternative water source.

The players

Trevor Cyran

Chief of the Civil Works project management office of the Baltimore District Corps of Engineers.

Eleanor Holmes Norton

D.C. Delegate who challenged the Corps' focus on only expanding the Dalecarlia Reservoir.

Tom Jacobus

Former general manager of the Washington Aqueduct who discussed alternative water sources in 2016.

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What they’re saying

“Expansion of the reservoir is not a secondary water source. With only a one day of backup water supply, human-made or natural events that make the river unusable would put residents, the District government and the regional economy at risk.”

— Eleanor Holmes Norton, D.C. Delegate (WTOP)

“We're trying to find a quick win that addresses some of the near-term issues, because they are quite, quite dire. The Dalecarlia expansion would add approximately 12 hours of water storage into the system. So, while we know that doesn't fix the problem, it improves the situation.”

— Trevor Cyran, Chief of the Civil Works project management office, Baltimore District Corps of Engineers (WTOP)

What’s next

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The takeaway

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