Lake Oswego Water Hardness & Quality Report (2026)

Lake Oswego, Oregon, in Clackamas County south of Portland — one of the most affluent and desirable communities in Oregon (Lake Oswego consistently ranks among Oregon's wealthiest and most sought-after residential communities — home of the eponymous Oswego Lake, a private lake accessible only to Lake Oswego residents), a major Portland south suburban community with excellent schools and a vibrant arts scene, and a picturesque Pacific Northwest community adjacent to the Willamette River and Tualatin Valley — draws its municipal water supply from the Clackamas River via the Lake Oswego–Tigard Water Partnership. Water hardness in Lake Oswego measures 23.5 mg/L — classified as very soft.

Lake Oswego's exceptional softness — among the softest in Oregon — reflects the Clackamas River's calcareous-poor Cascades volcanic watershed. The Clackamas River at North Clackamas County drains: the Western Cascades volcanic sequence (Eocene–Oligocene calcareous-poor Cascades volcanics — the Western Cascades' basalt, andesite, and tuff, calcareous-poor Fe-Mg silicate volcanic terrain); the Oregon Coast Range (Eocene calcareous-poor Siletz River Volcanics — calcareous-poor ocean floor basalt). The calcareous-poor Cascades volcanic watershed and effective Lake Oswego–Tigard Water Partnership treatment produce the exceptional 23.5 mg/L.

With hardness at 23.5 mg/L, Lake Oswego residents enjoy exceptionally soft water. Lake Oswego–Tigard Water Partnership consistently delivers water meeting all Oregon DEQ and EPA Safe Drinking Water Act requirements.