Plymouth Water Hardness & Quality Report (2026)

The City of Plymouth Public Works Department operates the water utility serving approximately 82,000 residents in Plymouth, Minnesota, located in Hennepin and western Carver Counties. Water is sourced exclusively from 17 municipal wells tapping the Prairie du Chien-Jordan aquifer system at depths of 302 to 473 feet. There are no surface water treatment plants; water is treated at wellhead facilities with aeration, filtration, and disinfection before distribution. The utility publishes an annual Consumer Confidence Report detailing compliance with EPA standards.

The supply originates from the Prairie du Chien Group aquifer in the Upper Mississippi River Basin watershed. Groundwater flows through Ordovician limestone and dolomite formations, including the Oneota Dolomite and Shakopee Formation, overlying the Jordan Sandstone aquifer. These carbonate-rich rocks naturally dissolve calcium and magnesium, resulting in a very hard supply at 411 mg/L with elevated mineral content; moderate iron is also present from the geologic matrix.

At 411 mg/L, this is a very hard supply that causes significant limescale buildup in pipes, water heaters, dishwashers, and washing machines, reducing efficiency and lifespan. Faucets develop white deposits and laundry feels stiff. Annual deliming and regular water heater flushing are recommended. A water softener is strongly recommended to prevent appliance damage. Water quality exceeds EPA standards per the 2024 report; notable detections include low arsenic (2.07–2.35 ppb), barium (0.15 mg/L), and fluoride (1.1–1.2 mg/L), all well below MCLs. Treatment uses chloramination, iron/manganese filtration, and corrosion inhibitors.