Tysons Water Hardness & Quality Report (2026)

Tysons, Virginia, in Fairfax County — an unincorporated Fairfax County urban center adjacent to McLean and the Beltway (I-495), one of the largest edge city commercial centers in the United States and the largest office concentration in the Washington DC area outside the capital itself — receives its municipal water from Fairfax Water, which draws from the Potomac River at the Corbalis and James J. Corbalis Jr. Water Treatment Plants, and from the Occoquan Reservoir, serving the Fairfax County northern corridor including Tysons.

The moderately hard 178.5 mg/L hardness and elevated TDS of 443.5 mg/L reflect the Potomac River watershed's mixed geology. The Potomac River above the Great Falls intake drains the Blue Ridge of Maryland-Virginia (soft Precambrian gneiss), the Great Valley (Ordovician Edinburg Limestone, Cambrian Conococheague Group dolomite — very carbonate-rich), and the Catoctin Formation (mafic metavolcanic). The Valley and Ridge carbonate tributaries (Shenandoah River — hard) blend with the soft Blue Ridge runoff, producing the moderately hard Fairfax Water supply throughout the northern Fairfax County area.

At 178.5 mg/L, Tysons's water is moderately hard — scale builds in kettles and appliances over months, dishwashers benefit from rinse aid, and bathroom fixtures develop calcium deposits. Quarterly descaling is appropriate. The PFAS level of 9.3 ppt is very high and warrants a certified reverse osmosis drinking water filter — the Quantico Marine Corps Base (AFFF user in the Occoquan-Potomac watershed), the Dulles Airport corridor (Dulles International Airport — AFFF user), and the Fairfax County defense-aerospace complex (Booz Allen, SAIC, DXC corporate military contractors) contribute to Tysons's elevated PFAS readings.