Johnson County, Iowa: drinking water report. Johnson County in eastern Iowa has a population of about 155,000, centered on Iowa City and the University of…
Johnson County in eastern Iowa has a population of about 155,000, centered on Iowa City and the University of Iowa. The Iowa River serves as the primary water source, supplemented by wells. The river drains a heavily agricultural watershed, and its water quality reflects the corn and soybean farming that dominates the surrounding counties. The Iowa City Water Division operates a state-of-the-art treatment plant, but the raw water it receives is among the most challenging in the state.
Nitrate in the Iowa River at Iowa City has been rising steadily. According to the Iowa DNR's 2024 source water monitoring data, the river exceeded 10 mg/L of nitrate – the EPA's MCL – on 42 days during the spring of 2024. Iowa City's treatment plant uses ion exchange to remove nitrate, adding significant operational cost. A 2023 University of Iowa Hygienic Laboratory study found that Iowa River nitrate concentrations during spring runoff have increased by 25% over the past two decades.
The EPA's UCMR5 data shows PFAS detections in the Iowa City system. The Iowa City Municipal Airport has used AFFF firefighting foam, creating a localized PFAS source. Disinfection byproducts also fluctuate seasonally, with the 2024 Consumer Confidence Report showing total trihalomethane levels peaking at 58 ppb during summer.
Iowa City's treatment plant does an effective job with difficult source water, but the margin of safety narrows during spring runoff season. A home reverse osmosis system eliminates nitrate concern at the kitchen tap entirely.
Check your water for current data on your area. For nitrate, reverse osmosis or ion exchange filters are effective. For PFAS and disinfection byproducts, activated carbon or RO both work. Our water filter guide explains the options. Pull your detailed report for seasonal data, and visit our Iowa page for statewide context.