McLean Water Hardness & Quality Report (2026)

McLean, Virginia is served by Fairfax Water, a regional utility providing drinking water to approximately two million residents in Northern Virginia. The utility operates two primary treatment plants: the James J. Corbalis Jr. Water Treatment Plant, drawing from the Potomac River with a treatment capacity of 225 million gallons per day, and the Frederick P. Griffith Water Treatment Plant, treating water from the Occoquan Reservoir at 120 million gallons per day. Both the Potomac River and Occoquan Reservoir serve as the primary sources for the McLean service area in Fairfax County.

The Potomac River and Occoquan Reservoir watersheds are underlain by Paleozoic carbonate and siliciclastic bedrock, including limestone and dolomite of Ordovician through Devonian age. As water flows over these mineral-rich formations it dissolves calcium and magnesium carbonates, producing naturally hard water. The Great Valley section's extensive carbonate deposits are the primary driver of McLean's hard supply. The Occoquan Reservoir, fed by the Bull Run and Occoquan rivers, drains similarly carbonate-rich terrain, further elevating mineral content.

McLean's water is classified as hard, typically ranging from 5 to 10 grains per gallon (84–170 mg/L as CaCO₃), causing scale buildup in kettles, water heaters, dishwashers, and washing machines, reducing efficiency and shortening equipment lifespan. Mineral deposits form on fixtures and reduce soap effectiveness. Many homeowners install point-of-use or whole-house water softeners to mitigate these effects, though softening is a personal choice rather than a health necessity. Fairfax Water consistently meets all federal and state standards, testing approximately 177 compounds, adding fluoride for dental health, and employing conventional filtration at both treatment plants.