Brookings Water Hardness & Quality Report (2026)

Brookings, South Dakota, in Brookings County on the Big Sioux River in the eastern South Dakota prairie — home to South Dakota State University and one of the state's most important agricultural research centers — receives its municipal water from the City of Brookings Water Treatment Facility, drawing from the Big Sioux River via a surface water intake or from local groundwater wells in the Big Sioux alluvium. The Big Sioux River drains the eastern prairie of South Dakota — one of the most mineral-laden agricultural drainages on the Great Plains.

The very hard 353.5 mg/L hardness and extreme TDS of 1,114.3 mg/L reflect eastern South Dakota's extraordinarily mineral-rich glaciated terrain. The Big Sioux watershed drains the James River Lowland and eastern Coteau des Prairies — landscapes blanketed with Quaternary calcareous glacial till (glacially pulverized Cretaceous limestone, chalk, and shale from multiple Pleistocene ice advances) overlying Cretaceous Pierre Shale and Niobrara Chalk Formation — among the most calcareous terrestrial deposits in North America. Agricultural drainage through this calcareous landscape further concentrates minerals in both surface runoff and groundwater, driving TDS to exceptional levels.

At 353.5 mg/L, Brookings students, faculty, and residents face very hard water as a consistent daily reality on the SDSU campus and throughout the community. Scale builds within days on all water contact surfaces, dishwashers produce scaled glassware without water softener treatment, and the elevated TDS produces a distinctly mineral taste in tap water. A whole-house water softener is effectively a household necessity in Brookings. An under-sink reverse osmosis unit dramatically improves drinking water quality from this very high TDS supply, producing noticeably cleaner-tasting water for this academic community.