Fairfax Water Hardness & Quality Report (2026)

Fairfax Water is a regional water utility serving most of Fairfax County, Virginia, and several adjacent jurisdictions. The utility draws raw water from two primary surface-water sources: the Potomac River and the Occoquan Reservoir, fed by the Occoquan River. Four treatment plants process this supply: the Frederick P. Griffith Jr. plant handles water from the Occoquan Reservoir, while the James J. Corbalis Jr., McMillan, and Dalecarlia plants treat water from the Potomac River. These plants feed an interconnected distribution system serving homes and businesses across Fairfax County and neighboring communities.

The Potomac and Occoquan watersheds span the Piedmont and Coastal Plain regions of northern Virginia, where surface water flows over and through Paleozoic sedimentary and metamorphic rocks, including limestones and shales. These carbonate-rich formations slowly release calcium and magnesium into the water as it moves through the watershed, contributing to a moderately mineralised character. The underlying geology, dominated by older sedimentary units, produces a supply that is naturally moderately hard, with stable mineral content influenced by seasonal flow and rainfall patterns.

At a moderately hard level, residents may notice light to moderate scale buildup on fixtures, showerheads, and inside appliances such as kettles, coffee makers, and dishwashers. Soap may not lather as freely as in softer water, and glassware may show faint white mineral deposits. Regular descaling and fixture cleaning can manage these effects; a water softener is generally optional rather than essential. Fairfax Water reports treated water consistently meets all federal and state standards, with testing for about 177 compounds; treatment includes coagulation, sedimentation, filtration through activated carbon and sand, chlorine disinfection, and addition of fluoride.