Mankato Water Hardness & Quality Report (2026)

Mankato, Minnesota, the Blue Earth County seat — a major south-central Minnesota city (the largest city in Greater Minnesota outside the Twin Cities metro area), home of Minnesota State University Mankato (MSU Mankato, a major Minnesota comprehensive university, home of the Mavericks), the Reconciliation Plaza (site of the largest mass execution in US history — the December 26, 1862 Dakota execution of 38 Dakota men), a major Minnesota River Valley agricultural, medical, and education hub — draws its municipal water supply from the Minnesota River via the City of Mankato Water Division. Water hardness in Mankato measures 99.5 mg/L — classified as moderately soft.

Mankato's moderate softness — much softer than the raw Minnesota River supply — reflects the City of Mankato's effective water treatment. The Minnesota River at Mankato drains through: the Coteau des Prairies and Wisconsin Age Des Moines Lobe calcareous till (highly calcareous glacial deposits from the Prairie Pothole region); the Minnesota River Valley Silurian–Ordovician calcareous dolomite substrate. The raw Minnesota River at Mankato is inherently very hard (typically 200–300 mg/L), but the Mankato water treatment plant applies effective softening (lime softening or ion exchange), substantially reducing hardness to the moderate 99.5 mg/L.

With hardness at 99.5 mg/L, Mankato residents enjoy moderately soft water for a Minnesota River Valley community. City of Mankato Water Division consistently delivers water meeting all Minnesota MDH and EPA Safe Drinking Water Act requirements.