Northwest One Water Hardness & Quality Report (2026)

DC Water serves Northwest One in Washington, D.C., providing water to the entire District including this neighborhood near NoMa and Union Station. The utility draws primarily from the Potomac River, with the Dalecarlia Water Treatment Plant treating river water from Great Falls and the Potomac Water Treatment Plant (part of Fairfax Water supply) handling additional river intake. Service covers all 68 square miles of DC, sourced from the Potomac Aqueduct system. No groundwater is used locally in Northwest One.

The Potomac River watershed spans 14,670 square miles across Maryland, Virginia, West Virginia, and DC, with headwaters in the Appalachian Mountains. Upper basin geology features folded Paleozoic sedimentary rocks rich in limestone and dolomite, while downstream Coastal Plain deposits include unconsolidated sands and gravels from the Potomac Formation. This mixed lithology imparts a moderately mineralized character to the surface water, with natural dissolution of alkaline earth metals shaping the chemistry before treatment.

Moderately hard water in DC leads to moderate scale buildup in dishwashers, washing machines, and water heaters, causing spotting on glassware and reduced efficiency over time. Faucets and showers may develop visible deposits, especially in warmer months. Regular vinegar descaling, rinse aids in dishwashers, and low-flow aerators help mitigate effects. A water softener is recommended for households with frequent spotting or appliance issues. DC Water maintains pH between 7.2–8.0 for corrosion control with full lead and copper rule compliance; no PFAS exceedances have been reported in recent monitoring, and the system records no primary standard violations.