Washington DC metro: water quality. The DC metro area is a jurisdictional puzzle for water supply.
The DC metro area is a jurisdictional puzzle for water supply. Washington DC itself is served by DC Water, which draws from the Potomac River and treats it at the Dalecarlia and McMillan plants. Arlington and Alexandria, Virginia sit just across the river but operate under the Virginia American Water and Alexandria Renew systems respectively. Baltimore, technically part of this metro's statistical area, runs an entirely separate system pulling from three reservoirs in the Gunpowder Falls watershed. With 6.3 million residents spread across DC, northern Virginia, and central Maryland, the metro spans three distinct regulatory environments – District, Virginia, and Maryland rules – each with different approaches to emerging contaminants.
The Potomac River, which supplies DC and much of northern Virginia, receives treated wastewater discharge from dozens of upstream communities. UCMR5 sampling has confirmed PFAS compounds in DC Water's finished water at detectable but low levels. The bigger concern in this metro centers on military installations. Joint Base Anacostia-Bolling in DC, Fort Belvoir in Virginia, and Aberdeen Proving Ground near Baltimore have all been identified by the Department of Defense as sites with PFAS contamination from AFFF use.
Maryland has proposed PFAS MCLs of 10 ppt for PFOA and PFOS individually. Virginia's Department of Health has been slower to act, relying primarily on federal standards. DC itself follows EPA guidelines. This regulatory patchwork means a resident in Bethesda, Maryland is protected by different standards than a neighbor in Arlington, Virginia – despite both cities drawing from Potomac-sourced systems.
A 2024 study published in Environmental Science & Technology Letters found that Potomac River PFAS concentrations fluctuated seasonally, with higher readings during low-flow summer months when wastewater effluent makes up a larger share of river volume.
DC's Potomac-sourced supply falls in the middle nationally. It lacks the pristine watershed advantage of cities like New York or San Francisco, but avoids the industrial groundwater contamination that plagues parts of Michigan, New Jersey, and the Carolinas. Baltimore's reservoir-based system generally tests cleaner for PFAS than Potomac-sourced water, though it faces its own lead infrastructure challenges.
Within the metro, the variation is striking. According to the Maryland Department of the Environment, some smaller water systems in Prince George's County have reported higher PFAS detections than the main DC or Arlington supplies. Check our DC state page and Virginia state page for jurisdiction-specific patterns.
Because this metro straddles three jurisdictions and multiple water systems, knowing your specific provider matters more here than in most places. A resident of Georgetown and a resident of College Park are under different utilities, different treatment plants, and different regulatory frameworks.
Check your water to identify your provider and see what recent monitoring has found. If you're near any of the military installations in this region, our report tool can show you whether contamination from those sites appears in your local water data. For filter recommendations tailored to Potomac River water chemistry, see our water filter guide.