Spearfish Water Hardness & Quality Report (2026)

Spearfish, South Dakota, in Lawrence County — a Lawrence County city adjacent to Lead and Deadwood in the northern Black Hills — receives its water from the City of Spearfish Water Department, drawing from Spearfish Creek and Black Hills aquifer wells through the west South Dakota distribution.

The hard 144 mg/L hardness and TDS of 340.9 mg/L reflect the Lawrence County Black Hills supply's hard calcareous character — the Cambrian Deadwood Formation is a calcareous sandstone and dolomite in the Black Hills limestone core, while the Precambrian Harney Peak Granite provides insoluble granitic dilution from the crystalline core (compare Lead SD: 140/332 in Lawrence County comparable; Deadwood SD: 148/350 in Lawrence County comparable; Spearfish consistent hard from the same Lawrence County Spearfish Creek Black Hills Cambrian calcareous supply). The Black Hills watershed — Cambrian Deadwood Formation (calcareous — primary hardness contributor), Precambrian Harney Peak Granite (insoluble — primary dilutant), and Quaternary Black Hills alluvium (slightly calcareous — minor TDS).

At 144 mg/L with TDS 341, Spearfish's water is hard — scale builds in appliances. Quarterly descaling is appropriate. The PFAS level of 1.8 ppt is very low — an excellent result for western South Dakota. Review the City of Spearfish's annual water quality report.