Gresham Water Hardness & Quality Report (2026)

Gresham, Oregon — the fourth-largest city in Oregon at the eastern edge of the Portland metropolitan area — receives its municipal water supply from the Portland Water Bureau, sourcing from the Bull Run Watershed — a 102-square-mile protected forest watershed on the slopes of Mount Hood in Clackamas County, managed exclusively for water supply. The Bull Run delivers water through two primary treatment facilities to the Portland metropolitan area, including Gresham in Multnomah County. Portland Water Bureau also has supplemental Columbia South Shore wellfield groundwater for peak demand. Water hardness in Gresham measures 81 mg/L — classified as moderately soft.

Gresham's moderately soft supply reflects the volcanic and Cascade Range geology of the Bull Run Watershed. The Bull Run drains the western slopes of Mount Hood and the upper Sandy River basin — terrain dominated by Quaternary and Tertiary Columbia River Basalt Group (CRBG) flows, Quaternary Mount Hood andesite and basaltic andesite volcaniclastic deposits, and older Oligocene–Miocene High Cascade volcanic sequences (andesite, dacite, and related volcaniclastics). These volcanic rocks — like most Pacific Northwest volcanic terrain — are mineralogically dominated by silica and alumina rather than calcium carbonate, contributing minimal dissolved calcium to watershed drainage. The cool, wet Pacific Northwest climate and the Bull Run's protected wilderness status ensure consistently high-quality, soft source water.

With hardness at 81 mg/L, Gresham residents experience minimal to moderate scale challenges. Faucet aerators and showerheads develop deposits slowly — bi-monthly cleaning with citric acid solution is sufficient. Dishwashers produce clean glassware with light rinse-aid use. Portland Water Bureau consistently delivers water meeting all Oregon DEQ and EPA Safe Drinking Water Act requirements.