Union Market Water Hardness & Quality Report (2026)

DC Water supplies the Union Market area of Washington, D.C., drawing its water predominantly from the Potomac River. This main source is augmented by water from the Patuxent and Occoquan Reservoirs, with a smaller contribution from groundwater. All of this water is processed at the Washington Aqueduct facilities, which are managed by the U.S. Army Corps of Engineers. These facilities serve a vast customer base, extending beyond the District to include parts of Arlington and Fairfax County in Virginia, totaling over 700,000 individuals.

The geology beneath the Potomac River watershed is a complex mix. It features sedimentary rock formations dating back to the Devonian and Ordovician periods, including the Keyser Limestone and various shales. Further downstream, the landscape transitions into the sands and gravels typical of the Coastal Plain. These rock types, particularly the limestones and shales, are known to dissolve and release minerals like calcium and magnesium into the water supply. This process results in a supply that is moderately mineralized, with concentrations often increasing during warmer months when river dilution is lower.

Homeowners in Union Market might notice some scale buildup in appliances like dishwashers, washing machines, and water heaters, which can lead to spotting on glassware and residue on fixtures. Devices such as kettles and coffee makers may benefit from a monthly descaling with vinegar. Installing drain screens can help capture any sediment. While a whole-house water softener is an option for those sensitive to the moderate mineral content, it's generally not considered essential. DC Water maintains strict adherence to EPA standards, including those for lead and copper, and recent tests show no PFAS exceedances. The water's pH is carefully controlled between 7.4 and 8.0.