Corvallis Water Hardness & Quality Report (2026)

The City of Corvallis Public Works Department supplies drinking water to approximately 60,000 residents in Benton County, primarily within Corvallis city limits and surrounding areas in the Willamette Valley. Water is drawn from two surface sources: the Willamette River via the Taylor Treatment Plant in southeast Corvallis, and Rock Creek via the Rock Creek Treatment Plant on the east side of Mary's Peak in the Oregon Coast Range. Both plants employ conventional treatment including coagulation, flocculation, sedimentation, filtration, and chlorine disinfection. The utility publishes annual Consumer Confidence Reports accessible via corvallisoregon.gov/publicworks.

The Willamette River basin is underlain by Tertiary marine sedimentary formations including the late Eocene to early Oligocene Spencer Formation and Keasey Formation—siltstones, sandstones, and shales with low solubility minerals. The Rock Creek Watershed drains forested foothills of the Oregon Coast Range, featuring Eocene volcanic rocks of the Siletz River Volcanics overlain by sedimentary layers. These low-carbonate geologies result in soft water, as rainwater and runoff interact with soils and rocks low in calcium and magnesium, yielding a supply with minimal dissolved solids.

Corvallis's soft water minimises scale buildup in pipes, water heaters, and appliances, reducing maintenance needs and extending equipment life without significant soap scum or spotting on fixtures. Dishwashers, washing machines, and faucets experience little mineral impact, and no water softener is recommended or necessary — routine flushing of hot water systems and basic cleaning suffice. Water quality meets all EPA standards with no violations; chromium (hexavalent) has been detected above health guidelines in some analyses but below legal limits, no PFAS or lead/copper exceedances have been reported, and pH is typically neutral to slightly alkaline post-treatment.