Quick take: the rule of thumb
The standard number says what kind of claim it is. The listing says which contaminants the exact model was tested for. For PFAS, you want NSF/ANSI 53 (carbon or ion exchange) or 58 (reverse osmosis), plus a PFAS line in the model’s listing. We don’t rank brands.
What to do
- Match the standard to your goal. Taste and chlorine point to 42. Health claims such as lead or PFAS point to 53 or 58.124
- Find the claim, not just the logo. A filter can be certified for taste and say nothing about PFAS. Look for “PFOA/PFOS” or “Total PFAS” in the listing.4
- Look up the exact model. EPA names five ANSI-accredited certifiers: CSA, IAPMO R&T, NSF, UL and WQA.5 Search the certifier’s database by model number. NSF’s listings are one example.7
- If the box says “P473,” check the current listing. NSF folded that older protocol into 53 and 58 and removed the P473 references.4
- Know what “certified” leaves out. As of April 2024, EPA said PFAS filter certifications don’t yet show that a filter removes PFAS down to EPA’s new drinking water limits.6
- Replace the cartridge on time. EPA says filters are only effective when maintained on the manufacturer’s schedule.6
Quick decoder
| If the label says… | What it tells you | Do | Don’t |
|---|---|---|---|
| NSF/ANSI 42 | Aesthetic effects: chlorine, taste and odor, chloramine, particulates, and similar.1 | Choose it if taste or chlorine is your goal. | Read it as a health or PFAS claim. |
| NSF/ANSI 53 | Health effects, with over 50 possible claims, such as lead, cysts and VOCs.1 NSF added PFOA/PFOS and “Total PFAS” claims for carbon and ion exchange filters.4 | Look for the specific contaminant in the listing. | Assume every 53 filter covers PFAS. Each listing names its claims. |
| NSF/ANSI 58 | Reverse osmosis systems. Total dissolved solids reduction is required, and other claims are optional, such as lead, arsenic, fluoride and VOCs.2 NSF added PFAS claims here too.4 | Look for a PFAS line in the listing. | Assume RO covers everything. Claims are listed per model. |
| NSF/ANSI 401 | Emerging or incidental contaminants, up to 15, such as certain drugs, herbicides and pesticides.1 | Use it as an extra, if one of those matters to you. | Treat it as a PFAS claim. The NSF page we read doesn’t list PFAS under it. |
| NSF Protocol P473 | An older NSF test method for PFOA and PFOS in home filters. NSF later folded it into 53 and 58.4 | Check the model’s current listing under 53 or 58. | Rely on an old “P473” mention alone. |
| NSF/ANSI 177 | Shower filters. It verifies chlorine reduction, which NSF calls an aesthetic effect. NSF says the same standard covers materials and construction.3 | Use it to judge chlorine claims on shower filters. | Read it as a PFAS claim. |
| “Tested” or “lab verified” with no standard | Depends entirely on the test. | Ask for the report: lab, standard, contaminants, date, model. | Accept a badge or an unnamed “independent test.” |
| “Removes 99% of contaminants” | Not a standard claim. | Ask “which ones, to what level?” | Treat it as proof. |
See the evidence: what the NSF and EPA pages say
What the standards cover. NSF describes 42 as aesthetic effects, 53 as health effects (over 50 claims) and 401 as emerging compounds and incidental contaminants.1 Standard 58 covers point-of-use reverse osmosis systems, with required total dissolved solids reduction and optional claims that include cysts, chromium, arsenic, nitrate/nitrite, lead, cadmium, barium, fluoride, copper, VOCs, asbestos, perchlorate, radium and selenium.2 The NSF 58 page we read doesn’t list microplastics among its claims.
How PFAS claims got into the standards. In 2016, EPA set a 70 ppt health advisory for PFOA and PFOS combined. NSF developed Protocol P473 to test home filters against it. In 2017 an NSF committee began folding P473 into standards 53 (carbon and anion exchange) and 58 (RO), and every P473 product and reference was replaced by 53 or 58. Updates in 2022 added a “Total PFAS” claim covering PFHpA, PFHxS, PFNA and PFBS, and lowered the combined limit from 70 ppt to 20 ppt.4
What’s still missing. In April 2024 EPA set legal limits of 4.0 ppt each for PFOA and PFOS. NSF said committees were working on updates to align 53 and 58 with that rule.4 EPA says that as of April 2024, certification standards didn’t yet show filters reduce PFAS to those levels.6 We didn’t check whether NSF has since published updated standards, so look at the date on any listing.
Shower filters. NSF/ANSI 177 verifies reduction of free available chlorine, which NSF classes as an aesthetic effect. NSF notes there are no federal regulations governing residential shower filters.3
Consumer Reports. CR advises choosing independently certified filters, typically NSF/ANSI 53 or 58, over a manufacturer’s unverified claim.8
Not medical advice
This guide explains labels. It doesn’t say whether any specific filter or water is safe for you. If you have a health concern, ask your clinician or local health department.
What we don’t know
- Whether NSF has updated 53 or 58 to match EPA’s April 2024 limits since the page we read was published. Check the standard’s current edition.
- How a certified model performs after months of real use. Certification tests the model, not your kitchen.
- Which models, if any, carry certifications from the other four certifiers. We didn’t search their databases.
Next: the water filter guide, what’s in your tap water and shower filters and PFAS.