Arlington Water Hardness & Quality Report (2026)

Arlington, Washington, in Snohomish County — a Snohomish County city adjacent to Marysville and Darrington, in the north Snohomish County corridor at the Stillaguamish River delta north of the Puget Sound — receives its municipal water from the City of Arlington Water Division, drawing from the Stillaguamish River at the Arlington water treatment intake in the Cascade foothills.

The very soft 51.5 mg/L hardness and TDS of 112.2 mg/L reflect the Stillaguamish River watershed's North Cascade volcanic character. The Stillaguamish River (North Fork and South Fork) drains the North Cascades of north Snohomish County — terrain underlain by Tertiary Cascades stratovolcanic rocks (Miocene-Oligocene Two Rivers Volcanics), Eocene Chuckanut Formation sandstone (arkosic sandstone — insoluble), and Precambrian metamorphic and crystalline core of the Cascades. All volcanic and silicic sedimentary source materials are largely insoluble, producing the very soft supply characteristic of the north Cascade River systems.

At 51.5 mg/L, Arlington's water is very soft — essentially no scale forms, soap lathers abundantly, and appliances maintain excellent efficiency. Annual descaling is sufficient. The PFAS level of 2.5 ppt is very good — the protected Stillaguamish watershed has limited direct PFAS industrial sources, with minor contribution from Paine Field (Everett, Snohomish County — Boeing aircraft manufacturing, AFFF use) in the lower Snohomish County corridor.