Rockville Water Hardness & Quality Report (2026)

The City of Rockville operates the Rockville Water Treatment Plant, serving approximately 70,000 residents in Rockville and parts of Montgomery County, Maryland. The primary water source is the Potomac River, drawn from the river's main stem. During maintenance, drought, or upgrades, the utility purchases supplemental water from the Washington Suburban Sanitary Commission (WSSC), which also sources from the Potomac. In 2024, supplemental purchases totaled approximately 5.6 million gallons, or 0.34% of annual production. The plant has a capacity of 8 million gallons per day and was upgraded to meet EPA standards. The 2024 Consumer Confidence Report is available via the Maryland Department of the Environment and at rockvillemd.gov/waterquality (PWS ID MD0150003).

The Potomac River watershed covers 14,670 square miles across Maryland, Virginia, West Virginia, and Pennsylvania, fed by tributaries including the Shenandoah and Monocacy. The geology features folded Appalachian strata — Devonian Marcellus Shale, Silurian Tonoloway Limestone, and Ordovician carbonates — which weather to release calcium and magnesium into the river. This mineral dissolution creates a hard supply with elevated alkalinity, shaped by the Piedmont region's mixed sedimentary and metamorphic rocks.

Hard water in Rockville causes limescale buildup on faucets, showerheads, and inside pipes, reducing water pressure and potentially clogging plumbing. Water heaters, dishwashers, and washing machines are most affected, with scale insulating heating elements and shortening appliance lifespan by 30–50%. Regular vinegar descaling helps, and a water softener is recommended to exchange calcium and magnesium ions. The 2024 CCR confirms compliance with all EPA and state standards; third-party testing noted Bromodichloromethane above health guidelines. Treatment at the Rockville Water Treatment Plant includes coagulation, sedimentation, filtration, and chlorination.