Oak Harbor Water Hardness & Quality Report (2026)

Oak Harbor, Washington, in Island County on Whidbey Island in Puget Sound — the largest city on Whidbey Island and home to Naval Air Station Whidbey Island (NAS Whidbey), one of the Pacific Northwest's major Navy aviation installations — receives its municipal water from the City of Oak Harbor Public Works Water Division, which draws from Cranberry Lake on Whidbey Island and supplements with imported Skagit River supply via the City of Anacortes water treatment system. Oak Harbor's island water supply is augmented by mainland Skagit County connections during high-demand periods.

The extremely soft 23 mg/L hardness and very low TDS of 38.7 mg/L reflect Whidbey Island's glacially scoured geology and the Skagit River's pristine Cascade Mountain drainage. Cranberry Lake on Whidbey Island drains the island's Pleistocene glacial till and outwash deposits over pre-Tertiary metamorphic basement — all non-carbonate terrains producing soft, low-mineral water. The Skagit River import drains the northern Cascade Range over metamorphic and volcanic rocks of the North Cascades crystalline complex — equally soft, glacier-fed water. Both supply sources produce extremely soft, low-TDS water characteristic of Puget Sound island and Cascade Mountain supplies.

At 23 mg/L, Oak Harbor's water is extremely soft — appliances and plumbing function at maximum efficiency. Scale is essentially absent, soap lathers instantly, and annual maintenance of heating appliances is sufficient. The important consideration for extremely soft water is mild corrosive character — the very low TDS and low buffering capacity mean water more readily leaches metals from older plumbing. In an older neighborhood or a home with copper or lead-solder plumbing, briefly flushing cold taps before drinking is prudent. The PFAS level of 1.6 ppt is excellent overall — however, residents should note that NAS Whidbey Island has been identified as a PFAS source site through historical AFFF use, and monitoring near the base boundary is ongoing. The 1.6 ppt city-wide average reflects the distance of the main city supply from the base contamination zone.