Downtown DC Water Hardness & Quality Report (2026)

DC Water is the public utility serving Washington, D.C., including Downtown DC, delivering drinking water sourced exclusively from the Potomac River. Raw water is withdrawn by the Washington Aqueduct, operated by the U.S. Army Corps of Engineers, from intakes at Great Falls and Little Falls, pumping approximately 140 million gallons daily. Treatment occurs at the Washington Aqueduct plant in Arlington, Virginia, before entering DC Water's distribution system of over 1,300 miles of pipes serving approximately 700,000 residents.

The Potomac River watershed originates in the Appalachian Mountains, carving through metamorphic rocks of the Blue Ridge, sedimentary layers of the Piedmont, and Coastal Plain sediments across roughly 14,670 square miles in West Virginia, Maryland, Virginia, and Pennsylvania. No groundwater aquifers directly supply the system; water chemistry is shaped by upstream limestone and dolomite formations from the Ordovician to Mississippian periods, which dissolve to impart a hard character with elevated calcium and magnesium. Seasonal variations occur as warmer months reduce dilution and concentrate minerals.

At 126 mg/L, hard water causes scale buildup in pipes, water heaters, dishwashers, and washing machines, reducing efficiency and lifespan, while producing soap scum, spotted glassware, and dry skin. Regular descaling with vinegar soaks and installing scale inhibitors are advised; a water softener or salt-free conditioner is recommended for affected households. DC Water's 2025 report confirms compliance with all EPA standards, including lead and copper rules managed via orthophosphate corrosion inhibitors. Trace Giardia and Cryptosporidium detected in source water are absent post-treatment; chlorine and chloramine disinfection is used, with recent reductions to improve taste. Nickel averages 0.8 ppb and sodium measures 19 ppm.