Reston Water Hardness & Quality Report (2026)

Fairfax Water is the principal utility serving Reston, Virginia, in Fairfax County, providing drinking water to over 2 million people across Northern Virginia. Water is sourced from the Potomac River, treated at the James J. Corbalis Jr. Treatment Plant (capacity: 225 million gallons per day), and from the Occoquan Reservoir, processed at the Frederick P. Griffith Treatment Plant (up to 120 million gallons daily). Reston receives blended surface water supplies from both sources through an extensive pipeline distribution network.

The Potomac River watershed spans 14,670 square miles from the Appalachian Mountains to Chesapeake Bay, with headwaters in West Virginia's limestone valleys. The Occoquan River and Reservoir draw from Fairfax and Prince William County tributaries within the Piedmont and Coastal Plain transition. Upstream Paleozoic carbonates — Devonian and Silurian limestones, dolomites, and shales — dissolve calcium and magnesium into the Potomac, while the Occoquan contacts Triassic sedimentary and metamorphic rocks, yielding a moderately mineralised supply with natural hardness from dissolved bicarbonates.

Moderately hard water leads to scale buildup in water heaters, dishwashers, and washing machines, reducing efficiency and increasing energy costs over time. Soap lathering is somewhat reduced, leaving spots on glassware and fixtures; regular descaling of heating elements annually and cleaning aerators monthly is advised. A water softener is often recommended for affected households. Fairfax Water meets all EPA standards; pH typically runs 7.2–8.0; treatment involves coagulation, sedimentation, filtration, and disinfection with chloramine. Trace contaminants such as bromodichloromethane have been detected above health guidelines per third-party analyses but remain below legal limits.