Franklin County, Ohio: drinking water report. Franklin County – Columbus and its suburbs – serves approximately 1.3 million residents.
Franklin County – Columbus and its suburbs – serves approximately 1.3 million residents. The City of Columbus draws from three reservoirs: Hoover, O'Shaughnessy, and Griggs, all fed by the Scioto River and its tributaries. The city operates three water treatment plants and provides wholesale service to several suburban communities. The Scioto watershed drains agricultural land across central Ohio, which shapes the contaminant profile of the source water.
Columbus faces a challenge common to Midwest cities drawing from agricultural watersheds: seasonal algal blooms that produce microcystins and other cyanotoxins. Ohio's experience with the 2014 Toledo water crisis – caused by a Lake Erie algal bloom – led to statewide investments in algal toxin monitoring. Franklin County's reservoirs are susceptible to blooms during warm, nutrient-rich conditions.
UCMR5 data shows low-level PFAS detections in the Columbus water system. Ohio does not have state-specific PFAS MCLs, relying on federal standards. According to the Ohio EPA's 2024 compliance data, the Columbus system met all federal contaminant limits but recorded disinfection byproduct levels that fluctuated seasonally with changes in source water organic content.
Seasonal variation is the key dynamic in Franklin County – water quality shifts with rainfall, temperature, and agricultural activity in the watershed.
Check your water for the latest monitoring data in your area. An activated carbon filter handles both disinfection byproducts and provides some PFAS reduction. Our water filter guide covers which certifications to look for. Pull your detailed report for seasonal trends, and visit our Ohio page for statewide data.
Drinking water is one exposure route. These federal datasets also cover Franklin County, OH.
The EPA places Franklin 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.
53% of homes in Franklin County, OH were built before 1980, and 15% 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 Franklin County, OH averages 8.8 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
Across 40 public water systems serving Franklin County, OH with EPA lead testing on record, 0 (0%) reported a 90th-percentile lead result above the EPA's 15 ppb action level, and the median is 2.4 ppb. 11 water systems serving Franklin County, OH carry a health-based EPA Safe Drinking Water Act violation.
| Most-cited violation type | Systems affected |
|---|---|
| Lead and Copper Rule Revisions | 5 |
| Total Trihalomethanes (TTHM) | 3 |
| Revised Total Coliform Rule | 2 |
| Nitrate | 1 |
| Haloacetic Acids (HAA5) | 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.