Lake Oswego Water Hardness & Quality Report (2026)

The City of Lake Oswego, Oregon, draws its drinking water exclusively from the Clackamas River, a highly protected source whose 940-square-mile watershed originates on the western slopes of Ollalie Butte near Timothy Lake in the Mount Hood National Forest. Water is treated at a state-of-the-art treatment plant utilizing conventional filtration plus ozone disinfection. The utility serves the Lake Oswego area in Clackamas County and surrounding communities, publishing an annual Consumer Confidence Report — the 2025 edition is available from the utility.

The Clackamas River watershed sits within the Cascade Range physiographic province, characterized by young Quaternary volcanic deposits overlying older sedimentary and metamorphic rocks. The watershed receives substantial runoff and snowmelt from high-elevation terrain, moving rapidly through volcanic and granitic geology. This young rock formation combined with high precipitation rates limits mineral dissolution — calcium and magnesium remain at low concentrations as water moves through the system — resulting in naturally soft water characteristic of the Pacific Northwest's Cascade region.

Soft water from the Clackamas River results in minimal scale buildup in pipes, fixtures, and appliances. Water heaters, dishwashers, and washing machines operate efficiently without mineral accumulation, and soap and detergent perform well — residents typically do not require water softening systems. Occasional sediment disturbance in distribution pipes may cause temporary discoloration; the utility recommends flushing with cold water to clear it. Under the fifth Unregulated Contaminant Monitoring Rule (UCMR 5), the utility monitors 30 chemical contaminants including 29 PFAS compounds and lithium; no detectable amounts have been found in Lake Oswego's drinking water. The tap water meets or exceeds all State and Federal safe drinking water standards.