Meridian Water Hardness & Quality Report (2026)

Meridian, Idaho, the second-largest city in Idaho in Ada County west of Boise, draws its municipal water supply from groundwater wells tapping the Treasure Valley Aquifer — the alluvial aquifer beneath the Boise Valley in Ada and Canyon Counties — through the City of Meridian Public Works Department Water Division. Meridian's wells access the Quaternary alluvial aquifer recharged by the Boise River and irrigation percolation in the Boise Valley. Water hardness in Meridian measures 113.5 mg/L — classified as moderately hard.

Meridian's moderate hardness reflects the Treasure Valley Aquifer's character in the western Ada County zone. The Treasure Valley Aquifer is recharged primarily by the Boise River — originating in the Idaho Batholith (Cretaceous Atlanta Lobe and Idaho Batholith granodiorite) and the Sawtooth Mountains granite in central Idaho — soft mountain crystalline terrain. However, the alluvial fill in the Treasure Valley, while derived from this soft granitic source rock, also incorporates sediments from the Columbia River Basalt Group (mafic volcanic rock) and the Tertiary lacustrine calcareous sediments (Lake Idaho Formation) that underlie the Snake River Plain. These calcareous lake sediments in the valley fill contribute moderate dissolved calcium to Treasure Valley groundwater, producing harder supply than the Boise River's mountain source alone.

With hardness at 113.5 mg/L, Meridian residents encounter moderate scale accumulation. Faucet aerators and showerheads develop deposits after several months — monthly cleaning with citric acid solution is practical maintenance. Dishwashers produce cleaner glassware with rinse-aid. City of Meridian Public Works consistently delivers water meeting all Idaho DEQ and EPA Safe Drinking Water Act requirements.