Cincinnati tap water: hard water, PFOS samples up to 6.1 ppt (EPA limit 4)

01 · What it means

What these readings mean for your home

Each reading in plain English: what it is, how Cincinnati compares with the other systems we track, and whether there’s anything to do. The tags follow EPA’s limits and reference levels where EPA has one; for hardness, which has no EPA limit, they follow the U.S. Geological Survey (USGS) scale and Minnesota’s health department. New to the acronyms? Every term, in plain English.

02 · The full results

Every PFAS result EPA recorded

In EPA’s national testing (sampled 2023 to 2024), Cincinnati’s highest samples reached PFOS at 6.1 ppt, above EPA’s 4 ppt limit. These are individual samples, not a compliance finding: water systems have until 2029 to meet the limit, judged on a yearly average.

03 · Where it comes from

The source, and who else drinks it

GCWW uses two sources: Ohio River water treated at the Richard Miller plant, which supplies about 88% of customers’ water, and groundwater from 13 wells in the Great Miami Buried Valley Aquifer treated at the Charles M. Bolton plant, which supplies about 12%.

Greater Cincinnati Water Works serves about 800,000 people directly, and 15 other water systems buy water from it, serving about 397,418 more. If you live in one of them, most of what’s on this page describes your water too, though hardness and disinfectant can change if your system blends in its own wells.

The Bolton plant adds lime to soften its groundwater, while the Miller plant uses granular activated carbon and UV light.

Cincinnati’s water system had no health-based violations in the five years through September 2026, according to EPA’s federal database.

04 · Questions

Cincinnati water questions

Is Cincinnati tap water safe to drink?

The U.S. Environmental Protection Agency (EPA) doesn’t grade a city’s tap water as safe or unsafe; it sets limits and records violations. By that record, Cincinnati’s water system had no health-based violations of federal drinking water rules in the five years through September 2026. Separately, EPA’s 2023–24 testing found PFOA or PFOS (two PFAS “forever chemicals”) samples above the 4 parts per trillion (ppt) limit that utilities must meet, on a yearly average, by 2029. A filter certified to NSF/ANSI 53 or 58 for PFOA and PFOS addresses it at the tap.

Is Cincinnati tap water hard?

Cincinnati tap water is hard: about 7.5 grains per gallon (128 milligrams per liter (mg/L)), depending on which treatment plant serves your neighborhood (126 to 140 mg/L), according to published water quality data from Greater Cincinnati Water Works (2025).

Does Cincinnati tap water have PFAS?

In the U.S. Environmental Protection Agency’s (EPA’s) national testing (sampled 2023 to 2024), Cincinnati’s highest samples reached PFOS (a PFAS “forever chemical”) at 6.1 parts per trillion (ppt), above EPA’s 4 ppt limit. These are individual samples, not a compliance finding: water systems have until 2029 to meet the limit, judged on a yearly average.

Does Cincinnati use chlorine or chloramine?

Free chlorine. Greater Cincinnati Water Works (GCWW) adds chlorine at both the Miller and Bolton plants, and its report lists the distribution residual as total chlorine.

Has Cincinnati’s water system had violations?

Cincinnati’s water system had no health-based violations in the five years through September 2026, according to the U.S. Environmental Protection Agency’s (EPA’s) federal database.