Merrifield Water Hardness & Quality Report (2026)

Merrifield, Virginia, in Fairfax County — a Fairfax County community adjacent to Falls Church and Annandale in north Virginia near the DC border — receives its water from Fairfax Water, drawing from the Potomac River (at the Corbalis and Griffith water treatment plants, Fairfax County) through the north Virginia distribution.

The hard 191 mg/L hardness and elevated TDS of 498 mg/L are harder than the Great Falls (169 mg/L) and other Fairfax Water communities — reflecting Merrifield's south Fairfax service zone which may draw more from the Griffith intake (a different Potomac blend ratio). The Potomac River at the Fairfax Water intake drains the Virginia Blue Ridge — Precambrian Catoctin Greenstone (insoluble), Triassic Culpeper Basin (calcareous redbed arkose — moderate hardness contributor), Cambrian Conococheague Formation (calcareous — primary hardness contributor), and Ordovician Beekmantown Group (calcareous). The Triassic and Cambrian calcareous input with higher concentration at the Griffith zone produces the hard north Virginia supply.

At 191 mg/L with TDS 498, Merrifield's water is hard — scale builds steadily in kettles and appliances, dishwashers benefit from rinse aid, and water heaters should be descaled annually. Monthly descaling is recommended. The PFAS level of 9.9 ppt warrants a certified reverse osmosis drinking water filter — Marine Corps Base Quantico (AFFF), Fort Belvoir (Fairfax County — AFFF), and the north Virginia Potomac corridor military-industrial PFAS complex contribute to Merrifield's very elevated readings.