Lewiston Water Hardness & Quality Report (2026)

The City of Lewiston Water Department and Lewiston Orchards Irrigation District (LOID) provide drinking water to Lewiston, Idaho, and surrounding areas in Nez Perce County. The supply is sourced from multiple groundwater wells tapping the alluvial aquifer beneath the Lewiston Orchards. Key facilities include wells along Powers Avenue and other sites serving residential, agricultural, and municipal needs. There are no surface water reservoirs or rivers as primary sources; treatment involves disinfection and basic filtration at wellhead facilities to meet EPA standards before distribution.

The watershed encompasses the Lower Snake and Clearwater River drainages, with groundwater recharged by precipitation and river infiltration in the Palouse-Clearwater highlands. Underlying geology includes thick layers of Miocene Columbia River Basalts interbedded with Quaternary glacial outwash sands and gravels forming the principal aquifer. This volcanic and sedimentary framework imparts a soft character to the water due to low natural mineralization from non-carbonate rocks, resulting in minimally mineralized groundwater with limited calcium and magnesium leaching from source rocks.

As a soft water supply, Lewiston experiences negligible scale buildup in pipes and appliances, reducing maintenance needs for water heaters, dishwashers, and laundry machines. Soap lathers easily without excess use, and spotting on dishes is rare. No water softener is required or recommended, though occasional sediment filtration may benefit well water users during high-turbidity events. Water quality testing by LOID and the City confirms contaminant levels well below EPA limits; the City of Lewiston's 2024 CCR confirms compliance with lead and copper rules. Chlorination provides microbial control, and monitoring covers disinfection byproducts and nitrates from agricultural runoff.