Northwest One Water Hardness & Quality Report (2026)

Northwest One, District of Columbia — the DC neighborhood encompassing areas around NoMa, Bloomingdale, and the Florida Avenue NW corridor near the McMillan Reservoir Sand Filtration Site — receives its municipal water from DC Water (DC Water and Sewer Authority), which draws from the Potomac River at the McMillan Reservoir system, treating water at the McMillan and Dalecarlia Water Treatment Plants in northwest DC before distribution throughout the District's water system.

The moderately soft 113.5 mg/L hardness and TDS of 254.7 mg/L reflect the Potomac River's characteristic water chemistry at Washington, DC. The Potomac drains a diverse watershed spanning from the Allegheny Highland and Blue Ridge Province (soft water from Precambrian crystalline terrain) to the Valley and Ridge Province (harder water from Ordovician and Cambrian carbonates via the Shenandoah River and Conococheague Creek), with the two components blending through the Piedmont Province in Maryland and Virginia before reaching the DC intakes. The resulting blend is a moderately soft supply reflecting the Piedmont's dilution of the Valley and Ridge carbonate input.

At 113.5 mg/L, Northwest One's water is moderately soft — characteristic of the DC Water supply throughout the District. Scale forms gradually in kettles and appliances over months, soap lathers well, and the dishwasher produces clean results without special treatment. Semi-annual to quarterly descaling of heating appliances is adequate. The PFAS level of 7.5 ppt warrants a certified drinking water filter — the DC metro area's dense federal agency, military installation, and industrial corridor presence contributes to elevated PFAS in the Potomac River watershed, though DC Water's treatment processes reduce finished water levels substantially.