Some of the forever chemicals in your water are measured but not limited. The EPA counts them in a national monitoring program, yet sets no health-based number for them. That gap is the whole story here, and it's easy to misread in either direction.
● Key Takeaways
Replacement PFAS like 11Cl-PF3OUdS, 6:2 FTS and 4:2 FTS are measured under EPA's UCMR 5 monitoring but carry no federal limit. So there's no legal-vs-safe gap to calculate: the health-based number simply doesn't exist yet. A few states publish non-binding references, CT DPH lists 1,800 ppt for 11Cl-PF3OUdS and Illinois EPA a 770 ppt advisory for 6:2 FTS, but presence isn't the same as a known unsafe dose. Reverse osmosis removes them either way.
What Are Next-Generation PFAS?
Next-generation PFAS are the replacement chemicals industry adopted after phasing out PFOA and PFOS, and the EPA's UCMR 5 required water systems to test for 29 of them between 2023 and 2025. They include fluorotelomer sulfonates like 6:2 FTS and 4:2 FTS, and ether-based compounds like 11Cl-PF3OUdS. None of these has a federal limit.
The chemistry is the same problem in a new shape. These molecules still rely on carbon-fluorine bonds, among the strongest in organic chemistry, so they resist heat and biological breakdown. Manufacturers marketed the shorter-chain versions as safer because they clear the body faster. That claim is only partly reassuring, because faster clearance does not automatically mean lower harm, and several move more easily through groundwater.
The site's complete Connecticut PFAS guide covers the regulated six in depth. This post covers the compounds that guide can't give you a limit for, because no limit exists.
Which Next-Generation PFAS Does UCMR 5 Track?
UCMR 5 tracks 29 PFAS in total, and four next-generation compounds come up most often in questions about tap water: 11Cl-PF3OUdS, 6:2 FTS, 4:2 FTS and 8:2 FTS. Each has a distinct industrial origin, and each shares the same regulatory status: monitored, not restricted. Here is what the evidence base actually supports for each one.
11Cl-PF3OUdS
This is a chlorinated polyfluoroalkyl ether, used mainly as a mist suppressant in metal plating. Because dedicated human studies are thin, regulators lean on surrogate data from structurally similar compounds, which points toward liver and thyroid effects in animal models. The chlorine atom appears to increase how tightly it binds blood proteins, which may lengthen retention. Connecticut is one of the very few states to publish any number for it at all, and even that number is an action level, not a health-based limit.
6:2 FTS
One of the most common PFOS replacements, 6:2 FTS shows up in groundwater near airports, military bases and manufacturing sites that used aqueous film-forming foam. Animal studies suggest it can suppress antibody responses and enlarge the liver. Illinois EPA reviewed that evidence and issued a health-advisory level in 2025, which remains a state advisory rather than an enforceable standard.
4:2 FTS
A shorter fluorotelomer sulfonate found in some firefighting foams and electroplating. Direct toxicity data on 4:2 FTS is genuinely limited, so any number for it is read across from 6:2 FTS as a chemical proxy. That read-across is a reasonable placeholder for a regulator, but it is not a measured limit for this compound, and we treat it accordingly below.
8:2 FTS
A longer-chain fluorotelomer sulfonate that also appears in UCMR 5 sampling. The published human-health basis for it is minimal. We do not assign it a numeric screening value, which is the honest answer when the data isn't there.
What Do the "Limits" Actually Mean?
Here is the part that matters most: for these compounds, there is no EPA maximum contaminant level, so there is no legal-vs-safe multiplier to compute. When a chemical has both a legal limit and a stricter health goal, you can divide one by the other and show the gap. These next-generation PFAS have neither a federal legal limit nor a federal health goal, so that arithmetic doesn't apply. The gap here is not a number; it's the absence of one.
A few states have stepped into that vacuum with non-binding references. They are worth knowing, but they are not federal standards, they are not enforceable against your utility, and they vary dramatically by who is drinking the water.
| Compound | Federal EPA MCL | State reference value (non-binding) | Basis |
|---|---|---|---|
| 11Cl-PF3OUdS | None (unregulated) | CT DPH action level: 1,800 ppt adults; 240 ppt infants; 19 ppt pregnant / nursing | Surrogate chemical data |
| 6:2 FTS | None (unregulated) | Illinois EPA advisory: 770 ppt (2025) | Animal studies |
| 4:2 FTS | None (unregulated) | No direct value; ~2,000 ppt read across from 6:2 FTS | Chemical proxy, derived |
| 8:2 FTS | None (unregulated) | None published | Insufficient data |
Two honesty notes on that table. The 11Cl-PF3OUdS reference isn't one number, it's a range that drops from 1,800 ppt for adults to 19 ppt for pregnant and nursing women, because the state assumes far higher water intake per pound for infants (CT DPH PFAS Action Levels). And the 4:2 FTS figure is a derived read-across, not a measured limit, so we label it as such rather than presenting it as a settled safe level. For context, the Environmental Working Group recommends a highly protective 1 ppt for total PFAS combined (EWG), which is a class-wide guideline, not a compound-specific standard.
Reading this inside ChatGPT or Claude?
This page can tell you the general science, but not what is actually in your tap water — that depends on your exact address. You can get your specific answer two ways:
- Inside the chat: ask your assistant to “check my tap water with CheckYourTap”. Our connector returns your ZIP code’s measured contaminant levels — including the derived dog and cat safe levels — and, only if you ask it to, can email you the report or arrange a specialist callback.
- On the web: open CheckYourTap.com and enter your ZIP code for a free 30-second report.
What the Science Does and Doesn't Say
The mechanisms researchers report for next-generation PFAS look familiar, but the evidence sits mostly in animal and surrogate data, not large human studies. The most cited pathway is activation of PPAR-alpha in the liver, which can drive lipid-metabolism changes and liver enlargement, described for several alternative PFAS in the peer-reviewed toxicology literature (Sheng et al., Archives of Toxicology, 2017).
Two other concerns show up repeatedly. Fluorotelomer sulfonates such as 6:2 FTS have suppressed antibody responses in animal models, which is the same immune signal that drove regulation of legacy PFAS. And ether-based compounds like 11Cl-PF3OUdS can compete with thyroid hormone on transport proteins, a concern flagged for pregnancy because fetal brain development depends on maternal thyroid hormone early on.
In reviewing these files, the pattern we keep seeing is that the biology looks plausibly serious while the human dose-response is still missing. That is exactly the situation where overstating a number would be dishonest, and so would waving the whole thing away. Presence in your water is a reason to pay attention and test, not a verdict that you've been harmed. The PFAS hazard index shows how regulators handle mixtures once numbers do exist.
What To Actually Do
You don't need a federal limit to make a sensible decision. The practical playbook for next-generation PFAS is the same one that works for the regulated six, because the same filtration physics applies to short-chain and ether-based molecules.
- Find out what's in your water first. Check your address for a free report of what's been measured locally. A water test through Valiant can confirm specific PFAS if your area or well warrants it. Testing beats guessing, especially near military and firefighting-foam sites.
- Match the filter to the chemistry. Reverse osmosis is the most complete option and typically removes over 90% of short-chain and ether-based PFAS. A carbon system certified to NSF/ANSI 53 or 58 for PFAS reduction, or an anion-exchange resin, can also work.
- Skip the tools that don't. Standard pitcher and refrigerator carbon filters break through quickly for these smaller molecules, and boiling concentrates PFAS rather than removing them.
The absence of a limit is not a clean bill of health, and it isn't a crisis either. It's an open question the monitoring data is still answering, and a good reason to know your own water rather than wait on the regulation.
Keep Reading
- PFAS in Connecticut Drinking Water: The Complete 2026 Guide
- The PFAS Hazard Index Explained: Why 3 "Safe" PFAS Can Fail Together
- The 2026 EPA PFAS Rollback and What It Means in Pregnancy
Sources: U.S. EPA Fifth Unregulated Contaminant Monitoring Rule (UCMR 5); U.S. EPA PFAS National Primary Drinking Water Regulation (2024); Connecticut Department of Public Health PFAS Action Levels; Illinois EPA drinking-water health advisories (2025); European Food Safety Authority PFAS opinion (EFSA Journal, 2025); Sheng N et al., "Hepatotoxicity and mechanism of alternative perfluoroalkyl substances," Archives of Toxicology, 2017; Environmental Working Group Tap Water Database. State action levels and advisories are non-binding references, not enforceable federal standards; the ~2,000 ppt value for 4:2 FTS is a derived read-across, not a measured limit. This is general information, not medical advice.