- Certification is granted per claim, not per standard. A filter “certified to NSF/ANSI 53” may be certified for exactly one contaminant. The standard name tells you almost nothing on its own.
- NSF/ANSI 401 does not include a single PFAS compound. Its claim list runs to 16 substances and PFOA, PFOS and their relatives are not among them. PFAS certification lives under 53.
- Three different PFAS numbers are in circulation and they are constantly confused. 70 ppt is an obsolete health advisory, 20 ppt is the certification testing threshold, and 4.0 ppt is the current EPA enforceable limit.
Why does this question have no simple answer?
Because the standard number and the actual protection are two different things, and the industry has no incentive to make that clear.
Here is the trap. NSF/ANSI 53 is the health-effects standard. It covers lead, cysts, VOCs, chromium, arsenic, PFAS and dozens more. But a manufacturer does not certify a product to “NSF/ANSI 53” as a whole. They certify it for specific named claims under that standard.
So a pitcher certified to NSF/ANSI 53 for cyst reduction and nothing else is, accurately and legally, “NSF/ANSI 53 certified”. It removes no lead. It removes no PFAS. The label is true and the impression it creates is false.
This single fact explains most of the confusion in this category, and it is why the rest of this guide is organised around claims rather than around standard numbers.
What does each standard actually cover?
| Standard | Covers | Health standard? | Typical claims |
|---|---|---|---|
| NSF/ANSI 42 | Aesthetic effects | No | Chlorine, taste, odour, particulate, iron, zinc |
| NSF/ANSI 53 | Health effects | Yes | Lead, cysts, VOCs, PFOA/PFOS, chromium, arsenic, turbidity |
| NSF/ANSI 58 | Reverse osmosis systems | Yes | TDS, arsenic, fluoride, hexavalent chromium, nitrate |
| NSF/ANSI 401 | Incidental / emerging compounds | Yes | Pharmaceuticals, pesticides, herbicides, bisphenol A |
| NSF/ANSI 177 | Shower filters | No | Chlorine only, one single claim |
| NSF/ANSI 244 | Supplemental microbiological | Yes | Bacteria, virus, cyst reduction |
| NSF/ANSI 55 | Ultraviolet treatment | Yes | Class A disinfection, Class B supplemental |
| NSF/ANSI 62 | Distillation systems | Yes | Arsenic, metals, nitrate, TDS |
The first thing worth noticing is that NSF/ANSI 42 is not a health standard. It exists so that a manufacturer can make a defensible claim about taste and smell. A filter certified only to 42 has made no verified health claim whatsoever, and a great many inexpensive pitchers and fridge filters sit exactly there.
The second is NSF/ANSI 177, which has exactly one claim in it: free available chlorine reduction. If you have bought a shower filter advertising heavy-metal removal, that claim is not coming from 177, because 177 contains no such claim to certify against.
Does NSF/ANSI 401 cover PFAS?
No. This is a flat no, not a nuance, and it is probably the most widely repeated error in the water filter category.
NSF/ANSI 401 is titled for incidental contaminants and emerging compounds, and the word “emerging” is doing a lot of damage. It sounds like it should be the modern-contaminants standard, and PFAS are the definitive modern contaminant, so the inference is natural. It is also wrong.
The complete 401 claim list contains 16 substances. They are pharmaceutical residues and consumer chemistry: ibuprofen, naproxen, estrone, bisphenol A, DEET, metolachlor, linuron, nonyl phenol, and similar. Not one of them is a PFAS compound. PFOA and PFOS are not in the list, and no perfluorinated or polyfluoroalkyl substance is.
So which standard actually covers PFAS?
NSF/ANSI 53. Effectively all of it.
There are two separate PFAS claims to distinguish, and the difference between them is significant when you are buying:
| Claim | What it means | Roughly how many certified products |
|---|---|---|
| PFOA/PFOS reduction | Two specific legacy compounds only | About 60 |
| Total PFAS reduction | A broader defined group of PFAS | About 49, all under NSF/ANSI 53 |
Two things in that table deserve emphasis.
First, Total PFAS Reduction certification sits under 53, and not one certified product carries it under 58. That is counterintuitive, because reverse osmosis is genuinely effective against PFAS as a technology. The gap is a certification gap, not a performance gap: the claim simply has not been pursued under 58 in the way it has under 53. If you are shopping for a certified PFAS claim specifically, you are shopping under 53.
Second, PFOA/PFOS reduction is a narrower claim than most buyers assume. PFAS is a family of thousands of compounds. A filter certified for PFOA and PFOS has been verified against two of them.
There is also a certification that no longer exists in the form you may see referenced. NSF P473 was retired in 2019 and folded into the NSF/ANSI 53 framework. If you encounter a product or an article still citing P473 as a current PFAS certification, that reference is at least seven years out of date.
And one genuine gap worth knowing: HFPO-DA, commonly known as GenX, has no certified reduction claim at all. Not under 53, not under 58, not anywhere. No product on the market is certified to reduce it. Any product implying otherwise is not making a certified claim.
Why are there three different PFAS numbers?
Because three different bodies set three different thresholds for three different purposes, and articles routinely collide them into one figure.
| Number | What it actually is | Status |
|---|---|---|
| 70 ppt | EPA lifetime health advisory, combined PFOA + PFOS | Obsolete. Superseded. |
| 20 ppt | The challenge concentration used in certification testing | Current, but a test protocol figure |
| 4.0 ppt | EPA enforceable maximum contaminant level for PFOA and for PFOS | Current regulatory limit |
The practical consequence: a certification test challenges the filter at 20 ppt and requires it to reduce the level below the certification endpoint. The EPA’s enforceable limit for public water systems is 4.0 ppt. These are answering different questions, and neither is the 70 ppt figure that still appears in older articles.
If you see a filter advertised as meeting “the EPA PFAS standard”, ask which number. The phrase is doing no work on its own.
Which standard covers fluoride?
NSF/ANSI 58 only. This one is short and worth stating clearly because it catches a lot of people.
NSF/ANSI 53 contains no fluoride reduction claim. None. If you want a certified fluoride reduction claim, you are looking at reverse osmosis under 58, or distillation under 62.
Carbon filters, pitchers and faucet mounts certified under 42 and 53 do not carry a certified fluoride claim, regardless of what the packaging suggests. Activated carbon is not an effective fluoride removal technology, and the certification landscape reflects that.
Is an NSF mark the only one that counts?
No, and this is one where buyers overpay unnecessarily.
NSF International is the standards writer, but it is not the only accredited certification body that can certify products to those standards. The Water Quality Association and IAPMO R&T both run accredited programmes against the same NSF/ANSI standards.
A WQA Gold Seal against NSF/ANSI 53 for lead reduction and an NSF mark against NSF/ANSI 53 for lead reduction represent the same standard and the same testing requirements.
This is not our characterisation of the relationship. In July 2023 the three bodies issued a joint letter on exactly this point, and NSF was a co-signatory to it. When the standards writer itself co-signs a statement that the other programmes are equivalent, the “only NSF counts” argument does not survive.
How do you check a product’s real claims?
This takes about two minutes and it is the only step that genuinely protects you.
- Find the model number. Not the product family name. The specific model, and the specific replacement cartridge, because certification attaches to the tested configuration.
- Search the certifier’s own listing database rather than the manufacturer’s website. NSF, WQA and IAPMO each publish searchable listings of certified products.
- Read the claim list, not the standard number. This is the whole exercise. “Certified to NSF/ANSI 53” is not information. “Certified to NSF/ANSI 53 for lead, cyst, and PFOA/PFOS reduction” is.
- Check the cartridge, not just the housing. A certified system running a non-certified generic replacement cartridge is no longer operating in its certified configuration.
- Match claims to your actual water. A PFAS claim is worth nothing to a household whose problem is hardness. If you have not tested, you are guessing about what you need.
That last point is the one most people skip. Certification tells you what a filter has been proven to do. It cannot tell you what your water needs removed.
Frequently asked questions
What is the difference between NSF 42 and NSF 53?
NSF/ANSI 42 covers aesthetic effects only: chlorine taste, odour and particulates. It is not a health standard. NSF/ANSI 53 covers health-related contaminants such as lead, cysts, VOCs and PFAS. A filter certified only to 42 has made no verified health claim.
Does NSF/ANSI 401 cover PFAS?
No. NSF/ANSI 401 covers 16 incidental compounds, chiefly pharmaceutical residues, pesticides and bisphenol A. No PFAS compound appears in its claim list. PFAS certification is granted under NSF/ANSI 53. The word “emerging” in 401’s title causes this error frequently.
Which NSF standard covers PFAS?
NSF/ANSI 53. Around 49 products hold Total PFAS Reduction certification and all of them are certified under 53, with none under 58. A separate and narrower PFOA/PFOS reduction claim covers about 60 products.
Does NSF 53 remove fluoride?
No. NSF/ANSI 53 contains no fluoride reduction claim at all. Fluoride reduction is certified under NSF/ANSI 58 for reverse osmosis systems, and under NSF/ANSI 62 for distillation. Carbon-based filters do not carry a certified fluoride claim.
What happened to NSF P473?
NSF P473 was the earlier standalone PFOA and PFOS protocol. It was retired in 2019 and folded into the NSF/ANSI 53 framework. Any current article or product listing still citing P473 as an active certification is out of date.
Is any filter certified to remove GenX?
No. HFPO-DA, commonly called GenX, has no certified reduction claim under any NSF/ANSI standard. No product on the market holds that certification. Claims about GenX removal are not certified claims.
Is a WQA Gold Seal as good as an NSF mark?
Yes, for the same standard and claim. The Water Quality Association and IAPMO R&T are accredited to certify against NSF/ANSI standards. In July 2023 NSF co-signed a joint letter with both bodies affirming the equivalence of the programmes.
What does NSF/ANSI 177 certify?
One thing: free available chlorine reduction in shower filters. It contains no other claim. A shower filter advertising heavy metal or chloramine removal is not making that claim under 177, because no such claim exists in the standard.
Why do PFAS limits show up as 70, 20 and 4.0 ppt?
They are three different things. 70 ppt was an EPA lifetime health advisory and is now obsolete. 20 ppt is the challenge concentration used in certification testing. 4.0 ppt is the current EPA enforceable maximum contaminant level for PFOA and for PFOS individually.
Does NSF certified mean the filter removes everything in the standard?
No, and this is the single most important thing to understand. Certification is granted per individual claim. A product certified to NSF/ANSI 53 may be certified for only one contaminant under it. Always read the specific claim list rather than the standard number.
Do replacement cartridges affect certification?
Yes. Certification applies to the tested configuration, which includes the cartridge. Running a certified housing with an uncertified generic cartridge means the system is no longer in its certified configuration, and the original claims no longer apply.
Which standard should I look for?
It depends entirely on your water. Chlorine taste is 42. Lead, cysts or PFAS is 53. Fluoride, nitrate or TDS is 58. Pharmaceutical residues is 401. Bacteria or virus is 244 or 55. Test your water first, then match the claim.
Related reading
- Well water testing cost by state (2026)
- How to test your water for PFAS
- How to test water quality at home
- Best water testing kits, ranked
Sources
- NSF certified product listings database, searched by standard and by claim, September 2026.
- NSF/ANSI/CAN 42, 53, 55, 58, 62, 177, 244 and 401 published scopes.
- US EPA, PFAS drinking water regulation, maximum contaminant levels for PFOA and PFOS.
- US EPA, 2016 lifetime health advisory for PFOA and PFOS (superseded).
- Joint statement on certification programme equivalence issued by NSF, the Water Quality Association and IAPMO R&T, July 2023.
- NSF announcement of the retirement of protocol P473 and its incorporation into NSF/ANSI 53, 2019.
