Gresham Water Hardness & Quality Report (2026)

The City of Gresham Environmental Services division manages drinking water for approximately 110,000 residents in Gresham and surrounding areas within Multnomah County, Oregon. The primary supply comes entirely from groundwater via the Cascade Well Field, a joint operation with Rockwood Water People's Utility District. Previously supplemented by Bull Run watershed surface water from the City of Portland, the transition to 100% groundwater occurred in late fall 2025. Columbia South Shore wells serve as a backup during high turbidity events. No separate named treatment plant is operated beyond standard well field extraction, disinfection, and processing.

Gresham's water originates from the Sand and Gravel Aquifer (SGA) within the Portland Basin, shaped by Pliocene-Pleistocene sedimentary deposits laid down 2 to 5 million years ago. Wells reach approximately 600 feet into layered sand and gravel strata, which overlie deeper basalt formations from volcanic activity. The aquifer's natural filtration through thick ancient sediments imparts a moderately mineralised character to the groundwater, distinguishing it from softer rainwater-influenced surface water supplies and contributing to slightly elevated mineral content compared to coastal sources.

As moderately mineralised water, Gresham's supply promotes moderate scale buildup in pipes, water heaters, dishwashers, and boilers, potentially reducing efficiency and increasing energy use over time. Maintenance tips include regular flushing of hot water systems, installing sediment filters, and vinegar descaling of faucets and fixtures. A water softener is optional but recommended for households noticing reduced soap lathering or dry skin, to extend appliance life and improve cleaning performance. The 2026 Drinking Water Quality Report confirms compliance with all EPA health guidelines, earning an A grade with no violations.