PFAS
PFOSPFOS
The health basis on which the EPA sets this contaminant's legal limit. Reported verbatim from the regulatory record — it is not a diagnosis or a prediction about any individual.
Liver and thyroid harm, immune suppression, increased cancer risk. A persistent "forever chemical" (MCLG = 0).
- Maximum contaminant level
- 4 ng/LLegal MCLEnforceable federal limit
- Health goal
- 0.0 ng/LHealth goal (MCLG)No safe exposure level
- Category
- PFASCategory
- Reporting unit
- ng/LReporting unit
Regulatory basis
How PFOS is regulated
What the enforceable limit actually obliges a utility to do, and how it differs from the health-based goal it is measured against.
Two different numbers govern PFOS, and they are not interchangeable. The Maximum Contaminant Level (MCL) is 4 ng/L — the enforceable ceiling. A system reporting above it is in violation and owes its customers notification and corrective action. The health goal (MCLG) is 0 and is not enforceable.
The health goal is zero. EPA sets a goal of zero when it has not identified a level at which the contaminant is known or expected to be free of the effects the standard was written to address. Zero is not attainable as an enforceable standard with available treatment technology and cost, so the MCL was set at 4 ng/L instead — the level EPA judged feasible. The practical consequence: a utility can report PFOS anywhere between zero and 4 ng/L and be fully compliant while still sitting above the health goal. “No violation” and “at the goal” are different statements about the same water.
Results are reported in ng/L. A laboratory result and the limits above are only comparable when both are expressed in that same unit — a value in a different unit will be off by orders of magnitude. WaterQualityLens groups PFOS under PFAS for navigation; the grouping is ours, the limits are the regulator’s.
The record for PFOS
- Enforceable limit (MCL)
- 4 ng/L
- Health goal (MCLG)
- 0
- Reporting unit
- ng/L
- Category
- PFAS
- Contaminant code
- PFOS
Limits as published by EPA and state primacy agencies. This page reports regulatory and certification records; it does not assess anyone’s exposure and makes no health prediction.
Certification scope
Which certifications actually remove PFOS
Only NSF/ANSI 53, 58 and 401 are health-contaminant standards. A product certified only to Standard 42 (aesthetics) or 372 (lead-free materials) has not been verified to reduce PFOS, however the box is worded.
NSF/ANSI 53
Counts — health standardHealth effects: lead, VOCs, cysts, chromium, and (post-P473) PFAS reduction.
2 filters in our registry hold an independently verified NSF/ANSI 53 claim for PFOS, listed below.
NSF/ANSI 58
Counts — health standardReverse osmosis: dissolved inorganics, arsenic, hexavalent chromium, and total PFAS.
4 filters in our registry hold an independently verified NSF/ANSI 58 claim for PFOS, listed below.
NSF/ANSI 401
Counts — health standardEmerging/incidental compounds: pharmaceuticals and select trace contaminants.
No filter in our registry holds a verified NSF/ANSI 401 claim for PFOS. That means we hold no certification record — not that the standard could never cover it.
NSF/ANSI 42
Does not count — not a health standardAesthetic effects: chlorine, taste, odor, particulates. No health-contaminant protection.
No registry product lists PFOS under NSF/ANSI 42. It would not count as verification of PFOS reduction in any case.
NSF/ANSI 372
Does not count — not a health standardLead-free materials (manufacturing content only). Not a water-treatment claim.
No registry product lists PFOS under NSF/ANSI 372. It would not count as verification of PFOS reduction in any case.
NSF/ANSI P473
Retired standardRetired 2022 PFOA/PFOS standard; absorbed into NSF/ANSI 53 and 58.
No current certification should rest on NSF/ANSI P473 alone. No registry product references it for PFOS.
Counts are of active products in the WaterQualityLens filter registry holding a verified claim for contaminant code PFOS under that standard, as recorded by the certifying body (NSF, WQA, or IAPMO). Certification is granted per contaminant, not per product: a filter certified to Standard 53 for one contaminant is not thereby certified for PFOS.
Certified reduction · commercial placements
Filters verified to reduce PFOS
These filters hold an independent NSF/ANSI health certification (Standard 53, 58, or 401) specifically for PFOS. Certification against a health standard means an accredited lab verified the filter reduces this contaminant — a materials-only claim such as NSF 42 or 372 does not.
- Verified PartnerZeroWater
5-Stage Ready-Pour Pitcher
ZW-ZD010RPPitcher$39.99NSF/ANSI 53Certified by IAPMO
- Verified PartnerLifeStraw
Home Water Filter Pitcher
LS-HOME7Pitcher$59.99NSF/ANSI 53Certified by IAPMO
- Verified PartnerClearly Filtered
Affinity Filtered Water Pitcher
CF-AFFINITYPitcher$90NSF/ANSI 58Certified by WQA
- Verified PartnerFrizzlife
M800 Under-Sink Reverse Osmosis
FZ-M800Under-sink RO$399NSF/ANSI 58Certified by NSF
- Verified PartnerAquaTru
Classic Countertop RO
AT-CLASSICCountertop RO$449NSF/ANSI 58Certified by NSF
- Verified PartnerWaterdrop
G3P800 Under-Sink RO
WD-G3P800Under-sink RO$549NSF/ANSI 58Certified by NSF
Hardware links are affiliate placements marked “Verified Partner.” Products appear here solely because they hold an independently verified NSF/ANSI health certification for PFOS; commercial arrangements never affect this list.