Herndon Water Hardness & Quality Report (2026)

Fairfax Water supplies Herndon, Virginia, drawing from two primary sources: the Potomac River and Occoquan Reservoir. Water is treated at the Potomac Treatment Plant near Lucketts, Virginia, and the Griffith Treatment Plant adjacent to Occoquan Reservoir. Fairfax Water serves over 2 million people across Northern Virginia, including the Town of Herndon, which does not operate its own utility but receives treated water through this regional provider. The Potomac River watershed spans 14,670 square miles, draining from the Appalachian Mountains to Chesapeake Bay.

The Potomac River flows through the Appalachian Piedmont and Coastal Plain provinces, where Paleozoic and Mesozoic sedimentary rocks — including limestone, shale, and sandstone from the Ordovician to Triassic periods — contribute dissolved minerals. The Occoquan Reservoir lies within the 600-square-mile Occoquan River basin, featuring Triassic sedimentary rocks and Quaternary alluvium. Limestone and dolomitic formations spanning from the Ordovician Martinsburg Shale to Cretaceous Coastal Plain deposits yield a moderately mineralised supply as calcium and magnesium ions dissolve into surface and shallow groundwater flows.

At moderately hard levels, water promotes scale buildup in pipes, water heaters, dishwashers, and coffee makers, reducing efficiency and lifespan. White mineral deposits appear on glassware, fixtures, and ice cubes. Periodic vinegar descaling of appliances and fixtures is recommended; commercial cleaners help remove stubborn residue. A water softener is often recommended for households experiencing frequent scaling to protect plumbing and improve soap efficiency. Fairfax Water maintains EPA compliance including the lead and copper rule via corrosion control, with treatment involving coagulation, sedimentation, filtration, and chloramination; recent Consumer Confidence Reports note no PFAS exceedances and the supply is considered safe for consumption.