Hamilton County, Ohio: drinking water report. Hamilton County – Cincinnati and its suburbs – serves about 830,000 residents.
Hamilton County – Cincinnati and its suburbs – serves about 830,000 residents. Greater Cincinnati Water Works (GCWW) draws from the Ohio River, which by the time it reaches Cincinnati has received discharges from Pittsburgh, Wheeling, and dozens of communities along its 981-mile course. GCWW operates one of the oldest continuously operating water treatment facilities in the country, with treatment upgrades added over the decades to address the river's complex and variable contamination profile.
The Ohio River is one of the most heavily utilized water sources in the eastern United States, and the contaminant mix at Cincinnati's intake reflects that. GCWW treats for a wide range of compounds, and the utility has invested in granular activated carbon filtration – unusual for a surface water plant – specifically to handle organic compounds and taste-and-odor issues.
UCMR5 data shows PFAS detections in the GCWW system. The Ohio River receives PFAS from upstream industrial discharges and municipal wastewater plants. According to the Ohio EPA's 2024 compliance data, GCWW's PFAS readings were below proposed federal MCLs, but the utility has flagged emerging contaminant monitoring as a priority.
The Ohio River's complexity means GCWW treats for more contaminants than most utilities. But individual building plumbing – particularly in Cincinnati's older housing stock – can introduce lead after water leaves the treatment system.
Check your water for data specific to your area. GCWW's carbon filtration already provides some PFAS reduction, but a home RO system adds another layer. Our water filter guide helps you decide what makes sense. Pull your detailed report, and see our Ohio page for statewide data.
Drinking water is one exposure route. These federal datasets also cover Hamilton County, OH.
The EPA places Hamilton 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.
74% of homes in Hamilton County, OH were built before 1980, and 32% 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 Hamilton 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
27 public water systems serving Hamilton 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. 10 water systems serving Hamilton County, OH carry a health-based EPA Safe Drinking Water Act violation.
| Most-cited violation type | Systems affected |
|---|---|
| Lead and Copper Rule Revisions | 4 |
| Lead and Copper Rule | 2 |
| Total Trihalomethanes (TTHM) | 2 |
| Stage 1 Disinfectants and Disinfection Byproducts Rule | 2 |
| 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.