North Potomac Water Hardness & Quality Report (2026)

North Potomac, Maryland, in Montgomery County in the affluent outer ring of the Washington, DC suburbs near Darnestown and the Potomac River, receives its municipal water from the Washington Suburban Sanitary Commission (WSSC), which draws from two major sources: the Potomac River treated at the Little Falls Water Treatment Plant near Bethesda, and the Patuxent River system managed through the T. Howard Duckett Reservoir. WSSC blends and distributes this supply throughout Montgomery and Prince George's counties, serving the full spectrum of DC suburban communities.

The moderately hard 140.5 mg/L hardness and TDS of 297.2 mg/L reflect the Potomac River's mixed watershed character. The Potomac draws water from its vast Valley and Ridge upper basin — the Shenandoah River tributaries drain through the classic Cambrian and Ordovician carbonate corridor of the Shenandoah Valley (Conococheague Limestone, Elbrook Formation, Beekmantown Group), contributing calcium and magnesium bicarbonate to the main stem river. The Piedmont tributaries of the lower Potomac basin add less hardness from their metamorphic terrain. WSSC's treatment processes moderate the seasonal variability in Potomac hardness into a consistent moderate supply.

At 140.5 mg/L, North Potomac's water is moderately hard — comfortable for everyday household use in this affluent suburban community. Scale forms gradually in kettles and water heaters over two to three months, the dishwasher produces clean glassware with rinse aid, and faucet aerators benefit from quarterly cleaning. Quarterly descaling of heating appliances is adequate. The PFAS level of 7.6 ppt warrants use of a certified drinking water filter for daily consumption — Montgomery County's dense technology, government contractor, and research corridor reflects in its elevated PFAS profile.