Ottumwa Water Hardness & Quality Report (2026)

Ottumwa, Iowa, in Wapello County in southeastern Iowa on the Des Moines River, receives its municipal water from the City of Ottumwa Water Works, drawing directly from the Des Moines River via a surface water intake in the south-central Iowa reach. The Des Moines River at Ottumwa has traveled over 400 miles from its headwaters in southwestern Minnesota and northwestern Iowa, passing through the glaciated Iowa drift plains and picking up dissolved minerals from every tributary and groundwater-fed baseflow along its journey. Ottumwa's water treatment plant processes this mineral-rich river water before distribution through the city's municipal grid.

The very hard 313.5 mg/L hardness and high TDS of 758.1 mg/L reflect the Des Moines River's cumulative carbonate burden from its long transit across the Iowa carbonate plains. The Iowa drift plain is underlain by Devonian and Mississippian carbonate formations — Burlington Limestone, Kinderhook Group, and associated limestones — deeply buried beneath Pleistocene glacial till composed of pulverized carbonate debris from multiple ice advances. Both tributary groundwater and direct carbonate bedrock contact throughout the watershed contribute very high calcium and magnesium bicarbonate loads to the river, producing consistently very hard water in communities drawing from the lower Des Moines.

At 313.5 mg/L, Ottumwa residents deal with very hard water requiring regular mineral management throughout the home. Scale accumulates aggressively in kettles and coffee machines, dishwashers leave heavy white deposits on glassware without softener treatment, and the mineral taste in tap water is pronounced at this TDS level. Water heater efficiency declines significantly without annual descaling. A whole-house water softener is highly recommended for Ottumwa households to protect plumbing and extend appliance life. The moderate PFAS level of 6.5 ppt also warrants use of a certified reverse osmosis unit for all drinking and cooking water.