PFAS in Southwest Ohio Drinking Water: What the Federal Limit Means

What is the federal PFAS limit in drinking water?

Four parts per trillion. In April 2024 the EPA finalized the first national drinking water standard for PFAS, setting an enforceable maximum contaminant level of 4.0 parts per trillion (ppt) for PFOA and 4.0 ppt for PFOS. The same rule set 10 ppt limits for PFHxS, PFNA and GenX (HFPO-DA), plus a hazard index limit that applies to mixtures of two or more of four compounds: PFHxS, PFNA, GenX and PFBS. PFBS is covered only through that mixture calculation. It has no individual limit of its own.

A part per trillion is a very small unit. Four ppt is four nanograms in a liter of water. EPA also set a health based goal of zero for PFOA and PFOS, but that is a goal, not a number any utility has to hit.

When does the PFAS rule actually get enforced?

April 26, 2029 is the date that matters. Before that, every public water system has to finish initial PFAS monitoring and report the results to its customers by April 26, 2027, and compliance monitoring starts then as well. Exceeding 4.0 ppt does not become a violation until 2029.

There is a live proposal to move that. On May 18, 2026 the EPA announced it would keep the 4.0 ppt limits for PFOA and PFOS while proposing a rule that lets a system request two more years, moving its compliance date from April 26, 2029 to April 26, 2031. It is opt in, not automatic. A system that wants the extension has to notify EPA by November 16, 2026. Under the same proposal, a system with a PFOA or PFOS result at or above 12 ppt would have to take short term steps to reduce exposure during the extension period.

EPA proposed a second rule at the same time that would rescind the drinking water regulations for PFHxS, PFNA, GenX and the hazard index mixture of those three plus PFBS. That would leave PFOA and PFOS as the only PFAS with federal drinking water limits.

The comment period on both closed July 20, 2026, and as of September 2026 neither one is final. What is not in question in either proposal is the 4.0 ppt number for PFOA and PFOS. The limit is holding. The deadline might slide.

Which southwest Ohio water systems test above 4.0 ppt?

These are the local systems with reported PFAS results above the federal limit:

- **Greater Cincinnati Water Works, Charles M. Bolton plant.** PFOA 5.0 ppt, PFOS 5.2 ppt. Bolton draws from the Great Miami Buried Valley Aquifer and serves roughly 12 percent of GCWW customers. - **Indian Hill Water Works.** PFOS 11.7 ppt. - **Clermont County, Miami, Goshen, Stonelick (MGS) plant.** PFOS 9.22 to 10.9 ppt. MGS is named for the three townships the plant serves. - **City of Dayton, Ottawa plant.** PFOS 8.81 ppt. - **City of Wilmington.** PFOS 8.79 ppt. - **City of Hamilton, South plant.** PFOA 5.30 ppt.

One caveat if you are in Cincinnati. GCWW runs two plants. The Richard Miller plant treats Ohio River water with granular activated carbon and UV, serves about 88 percent of GCWW customers, and is not on the list above. Bolton is. GCWW does not publish which plant feeds which address, so we are not going to tell you which one you are on. If you want to know, call GCWW and ask them directly.

Is that water safe to drink right now?

Legally, yes. None of the six systems above is in violation of anything today, because the 2024 limits are not enforceable until 2029 at the earliest.

The limits were built around lifetime exposure, meaning decades of drinking the same water every day, not around what a single glass does. A result of 11.7 ppt is close to three times the future limit, and that is worth knowing. It is not an emergency number. EPA's own proposed extension rule draws its short term action line at 12 ppt, which is above every result on that list.

Two practical notes. If you are on a private well, the federal rule does not cover you at all, and nobody is testing your water unless you pay for it. And if your household includes an infant on formula, filtering now is a reasonable call rather than waiting on a utility capital project that runs on a multi year timeline.

Does a water softener remove PFAS?

No. A softener is a cation exchange system designed to pull calcium and magnesium out of water. PFAS are not hardness minerals and a standard softener does not touch them. If someone quotes you a softener as a PFAS solution, they are selling you the wrong equipment.

What actually removes PFAS from tap water?

EPA names four best available technologies for PFAS: granular activated carbon, anion exchange, reverse osmosis and nanofiltration. Nanofiltration is a plant scale technology. The other three all exist in home versions.

For a house, two certified options matter:

- **A carbon block filter certified to NSF/ANSI 53 for PFOA and PFOS reduction.** This is the cheap route. Pitcher, faucet mount or under sink. It works as long as you actually change the cartridge on schedule. - **A reverse osmosis system certified to NSF/ANSI 58 for the same claim.** Higher up front cost, less frequent maintenance, and it reduces a much longer list of contaminants at the same time.

NSF announced in May 2019 that both NSF/ANSI 53 and NSF/ANSI 58 carry PFOA and PFOS reduction claim requirements. This part matters: a filter can carry NSF/ANSI 53 or 58 certification without carrying the PFOA and PFOS claim, because those standards cover many separate contaminant claims. Ask for that claim by name and confirm it on the manufacturer's certification listing before you buy.

An under sink RO unit forces water through a semi permeable membrane that rejects the large majority of PFAS molecules. No home filter is a total barrier, and any product sold as one is overselling.

Whole house RO exists but is expensive and wastes a lot of water for what most homes need, since PFAS exposure from water comes mostly through drinking and cooking. Treating the kitchen tap covers that at a fraction of the cost.

RO runs at plant scale too, though locally it has gone in for hardness rather than for PFAS. Greene County phased in a reverse osmosis plant through March 2024 and dropped from 27 grains per gallon to 8. Harrison fully activated its RO softening plant on October 3, 2022 and went from 21 gpg to 8.

Hard water and PFAS are two different problems

Do not let a PFAS conversation turn into a hardness sale, or the reverse. The Water Quality Association bands hardness this way: 0 to 3.5 grains per gallon is soft, 3.5 to 7 is moderate, 7 to 10.5 is hard, and anything above 10.5 is very hard.

Most of this region lands in the hard band. GCWW is 7.4 gpg at Miller and 8.2 at Bolton. Butler County Water is 7.7, Hamilton 7.6, Fairfield 7.7, Warren County 8, Greene County 8, Harrison 8, Dayton 8.1 including Kettering and Centerville, Indian Hill 8.8 to 9.9, Wyoming 10.1. Northern Kentucky Water District averages about 7.3 and swings between 4.6 and 9.8 with the season.

A few places are genuinely very hard. Xenia runs 23 gpg. Oxford runs 20 to 22. Aurora, Indiana is 21.05. Those homes usually notice a softener right away.

Some systems do not publish a hardness figure at all, including Middletown, Springboro, Trenton, Loveland, Wilmington, plus Lawrenceburg and Batesville in Indiana. If you are on one of those, a test at your own tap is the only way to know.

None of those numbers say anything about PFAS. Hardness causes scale and soap problems. PFAS is a health limit. Different problem, different equipment.

What we install and what it costs

Our Complete Home System is $3,492 installed, flat rate. That is softening for the hardness plus reverse osmosis at the kitchen sink for drinking and cooking. Lifetime tank warranty, five year valve. Installation is free on garage, basement and utility closet installs. The RO filter change runs $199 a year.

Here is the honest version of the sales pitch. If PFAS is the only thing you care about, a carbon block filter certified to NSF/ANSI 53 for PFOA and PFOS is cheaper than anything we sell, and you should buy that instead. Our system is worth it when you have both problems at once. Hardness is the common one across this region. PFAS above 4.0 ppt has been reported at six systems, so if you are on one of those you have both, and that is when a softener plus RO is the right buy.

Call and give us your address. We will tell you whether your system is one of the six reporting above 4.0 ppt, and what your hardness number is, before anyone talks about equipment. Honest Water Ohio, Cincinnati, (513) 466-0716.