Warren County, Ohio: drinking water report. Warren County between Cincinnati and Dayton has about 239,000 residents in fast-growing communities like Mason,…
Warren County between Cincinnati and Dayton has about 239,000 residents in fast-growing communities like Mason, Lebanon, and Springboro. Water comes from the Great Miami Aquifer and the Little Miami River watershed, with Warren County Water and Sewer Department and city systems serving different areas. The county's rapid suburban growth is replacing farmland with development, but the agricultural contamination in the aquifer persists.
The Great Miami Buried Valley Aquifer in Warren County shows the same vulnerability documented upstream in Butler and Montgomery Counties. According to the Ohio EPA's 2024 source water assessment, nitrate and atrazine from agricultural activity are detected at low but consistent levels in monitoring wells, reflecting decades of farming before suburban conversion.
The former Clinton County Air Force Base (now Wilmington Air Park) in neighboring Clinton County has PFAS contamination that may affect the regional aquifer system. Ohio EPA's 2024 investigation found PFAS at 8 ppt in Warren County monitoring wells near the county's eastern border. The EPA's UCMR5 data showed low-level PFAS in two Warren County water systems.
Warren County's rapid growth means new homes are often built over former farmland where decades of chemical application have left residues in the aquifer. Municipal systems treat for these contaminants, but if you are on a private well in a recently developed area, the aquifer still reflects its agricultural past.
Check your water for current data. For the combination of agricultural legacy and emerging PFAS, reverse osmosis provides comprehensive household protection. Our water filter guide covers systems suited to Ohio aquifer water. Pull your detailed report for trends, and visit our Ohio page for statewide context.
Drinking water is one exposure route. These federal datasets also cover Warren County, OH.
The EPA places Warren County, OH 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.
33% of homes in Warren County, OH were built before 1980, and 8% 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 Warren County, OH averages 9.1 µg/m³, above 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
22 public water systems serving Warren County, OH 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. 5 water systems serving Warren County, OH carry a health-based EPA Safe Drinking Water Act violation.
| Most-cited violation type | Systems affected |
|---|---|
| Lead and Copper Rule Revisions | 3 |
| Revised Total Coliform Rule | 2 |
| Lead and Copper 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.