Oak Hill Water Hardness & Quality Report (2026)

Oak Hill, Virginia, an unincorporated community in Fairfax County — a major north Fairfax County community (Oak Hill is a significant affluent unincorporated Fairfax County community in the Reston–Herndon corridor — one of the higher-income communities in the greater Washington DC area's northern Virginia technology corridor), adjacent to Reston and Herndon in the Dulles Technology Corridor (the Dulles corridor in northern Virginia is one of the most significant technology and defense contracting employment zones in the United States, with major data centers, tech companies, and federal contractors throughout the Reston–Herndon–Oak Hill area), a diverse Fairfax County community with a significant South Asian-American, Korean-American, and Latin-American population, and a community directly adjacent to Dulles International Airport — draws its municipal water supply via Fairfax Water. Water hardness in Oak Hill measures 114.5 mg/L — classified as moderately hard.

Oak Hill's moderate hardness reflects Fairfax Water's Occoquan Reservoir supply and the north Fairfax County distribution characteristics. The Occoquan Reservoir (Bull Run watershed) drains the Northern Virginia Piedmont (Precambrian–Paleozoic calcareous-moderate Bull Run Mountains and Fairfax County gneiss). Fairfax Water distributes to the Oak Hill–Reston north Fairfax zone (primarily 1970s–1990s suburban development mains), producing the moderate 114.5 mg/L.

At 114.5 mg/L, Oak Hill residents encounter moderate scale accumulation. Monthly cleaning with citric acid solution is recommended. Fairfax Water consistently delivers water meeting all Virginia DEQ and EPA Safe Drinking Water Act requirements.