Riley County, Kansas: drinking water report. Riley County in northeast Kansas has about 74,000 residents, with Manhattan – home to Kansas State University
Riley County in northeast Kansas has about 74,000 residents, with Manhattan – home to Kansas State University – as the primary city. The City of Manhattan draws from Tuttle Creek Lake and the Kansas River, with a treatment plant upgraded in recent years to handle the region's challenging source water. Fort Riley, a major Army installation, occupies a large portion of the county's western half.
Tuttle Creek Lake frequently experiences harmful algal blooms during summer and fall. According to the Kansas Department of Health and Environment's 2024 lake monitoring report, microcystin concentrations at the Manhattan intake exceeded 5 ug/L during September 2024 – well above the 1.6 ug/L health advisory for drinking water. Manhattan's treatment plant uses powdered activated carbon and enhanced oxidation to manage cyanotoxins during bloom season.
Fort Riley has confirmed PFAS contamination from AFFF firefighting foam. KDHE's 2024 PFAS investigation found PFOS at 28 ppt in monitoring wells near the base's fire training areas. The contamination affects groundwater in the area between Fort Riley and Manhattan, where some properties rely on private wells.
Manhattan's water treatment handles algal toxins during bloom season, but the intensity of the blooms means the system operates under stress during late summer. A household carbon filter provides an extra buffer during peak bloom months.
Check your water for seasonal data. For cyanotoxins and PFAS, reverse osmosis addresses both. Our water filter guide covers systems suited to lake-sourced water in algal-bloom-prone regions. Get your detailed report for seasonal trends, and visit our Kansas page for statewide data.
Drinking water is one exposure route. These federal datasets also cover Riley County, KS.
The EPA places Riley County, KS in Zone 1 - the EPA's highest-risk category, where the predicted average indoor radon level is above 4 pCi/L. Zone maps predict an area's radon potential from geology and existing indoor readings; they say nothing about a specific house. Testing is the only way to know your own level.
45% of homes in Riley County, KS were built before 1980, and 12% before 1950. Residential lead paint was banned in 1978, so housing age is the strongest available proxy for lead-paint exposure. This describes the county's housing stock, not any one home.
Modelled annual fine-particle pollution (PM2.5) in Riley County, KS averages 7.4 µg/m³, within the EPA's annual standard of 9 µg/m³. These are CDC modelled county estimates rather than readings from a specific monitor.
How radon zones work · Air quality by county · Lead exposure guide
13 public water systems serving Riley County, KS have EPA lead testing on record. The reported lead sample skews toward systems that already flagged a problem, so its exceedance rate is not directly comparable with other areas. 4 water systems serving Riley County, KS carry a health-based EPA Safe Drinking Water Act violation.
| Most-cited violation type | Systems affected |
|---|---|
| Lead and Copper Rule | 2 |
| Total Trihalomethanes (TTHM) | 1 |
| Revised Total Coliform Rule | 1 |
Source: EPA Lead and Copper Rule 90th-percentile tap sampling and EPA SDWIS Safe Drinking Water Act enforcement records, aggregated from the public water systems serving this county. Figures are counts of water systems, not a test of any individual home or tap.