Does reverse osmosis remove PFAS, fluoride, lead, nitrate, arsenic, bacteria, microplastics and sodium? One table, by NSF/ANSI claim
RO removes a contaminant only when its NSF/ANSI 58 or 53 listing names it: lead passes at 5 ppb, PFOA/PFOS at 20 ppt. Bacteria is NSF/ANSI 55 UV, not RO.
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Short answer
A home reverse osmosis system removes a contaminant only when its NSF/ANSI 58 or NSF/ANSI 53 listing names that contaminant. NSF’s fact sheet on NSF/ANSI 58 lists total dissolved solids reduction plus optional claims for cyst, chromium, arsenic, nitrate/nitrite, cadmium and lead. Lead is tested with 150 ppb challenge water and must leave 5 ppb or less, per Wastewater Digest’s report on the revised standard; PFOA and PFOS pass at 20 ppt each under NSF/ANSI 53, per the Pennsylvania DEP list. One NSF/ANSI 58 fluoride listing cites a maximum product-water concentration of 1.5 mg/L against EPA’s 4.0 mg/L MCL. Reverse osmosis carries no bacteria claim: that is NSF/ANSI 55 Class A ultraviolet at 40 mJ/cm². Dissolved gases such as radon, chloramine and most VOCs need a carbon stage, which EPA credits with up to 99.9 percent VOC removal. Softened feed water is fine: Express Water states its membrane removes 98 percent of the sodium a softener adds. Read the unit’s own listing before you buy.
If your lab report says coliform or your complaint is a rotten-egg smell, this is the wrong page: RO carries no bacteria claim and gases pass the membrane, so read the coliform guide or the rotten-egg smell guide instead.
Does reverse osmosis remove it? The table
A reduction claim is a contaminant named in a unit’s certified listing, tested against a stated challenge concentration and required to leave the water at or below a stated pass level. Where a source publishes no number, the cell says so.
| Contaminant | Standard | Test challenge | Pass or reduction level | Notes |
|---|---|---|---|---|
| PFOA / PFOS | NSF/ANSI 53 (some certifiers write it into 58) | Not published on a primary source read for this page | 20 ppt each, combined not to exceed the total, per Pennsylvania DEP | NSF’s 58 fact sheet does not name PFAS; full detail in the PFAS guide |
| Fluoride | NSF/ANSI 58 | Not uniform across listings | 1.5 mg/L maximum product water, per one NSF certified listing (R.E. Prescott ELP50-4) | EPA MCL 4.0 mg/L; see the fluoride guide |
| Lead | NSF/ANSI 53 or 58 | 150 ppb | 5 ppb, per Wastewater Digest | EPA action level 0.015 mg/L now, 0.010 mg/L from 1 November 2027; see the lead guide |
| Nitrate / nitrite | NSF/ANSI 58 | Not published in the NSF listing | Listing says “at or below the referenced concentration”; no percentage | EPA MCL 10 mg/L as nitrogen; see the nitrate guide |
| Arsenic | NSF/ANSI 58 | Not published on a primary source read for this page | Claim is arsenic V only | EPA MCL 0.010 mg/L; see the arsenic guide |
| Bacteria, viruses, cysts | Not an NSF/ANSI 58 claim; NSF/ANSI 55 Class A UV | Live organism challenge per NSF protocol | 40 mJ/cm² UV dose at highest achievable flow, per Fresh Water Systems | Reviewed in the UV purifier review |
| Microplastics | No dedicated standard; NSF/ANSI 42 Class 1 particulate as surrogate, accepted under NSF/ANSI 401 | 0.5 to 1 µm particulate | No fixed minimum found; one certified maker (Coway) claims over 99 percent | A separate microplastics guide is in progress on this site |
| Sodium from a softener | Not a named claim; falls under TDS reduction | Not applicable | About 98 percent of softener-added sodium, per Express Water | Product-water taste and pH: remineralization guide |
What does the number mean?
A pass level is the highest concentration allowed in the product water during the certification test, and it is a laboratory figure, not a promise about your tap. NSF’s fact sheet states that NSF/ANSI 58 covers structural integrity, material safety and TDS reduction, with the contaminant claims as optional extras a maker chooses to test for.
That is why the answer to “does RO remove X” is always “which unit”. Two RO systems with the same membrane can carry different listings, and the one that never paid for the arsenic test has no arsenic claim, whatever the membrane does in practice.
The EPA figures in the table are the numbers that decide whether treatment is needed at all: 0.010 mg/L for arsenic, 10 mg/L as nitrogen for nitrate, 4.0 mg/L for fluoride, and a lead action level of 0.015 mg/L today and 0.010 mg/L from 1 November 2027. All come from EPA’s National Primary Drinking Water Regulations, and the full list is on the EPA limits table.
One gap to be honest about: the minimum TDS reduction NSF/ANSI 58 requires is quoted widely, but no primary source reachable for this page confirmed the figure, so this page states only that the standard tests TDS reduction.
What does RO not do without another stage?
The membrane rejects dissolved ions and particles; it is not the technology EPA names for gases or volatile organics. EPA’s overview of treatment technologies credits reverse osmosis with inorganics, dissolved solids, radionuclides and synthetic organic chemicals, and credits granular activated carbon with up to 99.9 percent removal of many VOCs.
| Category | Why RO alone underperforms | What to add |
|---|---|---|
| Dissolved gases (radon, carbon dioxide) | Gas molecules pass the membrane; EPA’s archived radon page states there is no federally enforced drinking-water standard for radon, only a 1999 proposal of 4,000 pCi/L or 300 pCi/L that was never finalized | Aeration, or a carbon stage; see the uranium and radon guide |
| Chloramine | Passes most thin-film membranes and attacks them; no RO listing carries a chloramine claim | Catalytic carbon pre-filter; see the chlorine and chloramine guide |
| VOCs | The RO listing carries no VOC claim; EPA’s cited technology is GAC at up to 99.9 percent | Carbon pre-filter or a standalone GAC stage |
| Bacteria, viruses, cysts | No such claim under NSF/ANSI 58 beyond optional cyst reduction | NSF/ANSI 55 Class A UV at 40 mJ/cm² |
Most under-sink RO systems ship with one or two carbon pre-filters, which is where the chloramine and VOC work happens. When those cartridges go out of date, the membrane is on its own.
Which treatment class fits?
| Your lab result | Treatment class | Why |
|---|---|---|
| PFOA or PFOS above 4.0 ppt | RO or carbon block with PFOA/PFOS named in an NSF/ANSI 53 listing | The 20 ppt acceptance level per Pennsylvania DEP is the pass mark; the PFAS guide explains why 4.0 ppt is the number to beat |
| Lead above 0.015 mg/L | RO or carbon block with a lead claim | 150 ppb challenge, 5 ppb pass, per Wastewater Digest |
| Nitrate above 10 mg/L as N | RO with a nitrate/nitrite claim | The listing sets a maximum feed concentration, so check yours is at or below it |
| Arsenic above 0.010 mg/L | RO with an arsenic claim, after speciation | The claim covers arsenic V only |
| Fluoride above 4.0 mg/L, or any level you want lowered | RO with a fluoride claim | One listing cites 1.5 mg/L maximum product water |
| Coliform present | NSF/ANSI 55 Class A UV, not RO | 40 mJ/cm² dose per Fresh Water Systems; RO has no bacteria claim |
| Radon, chloramine or VOCs | Aeration or carbon stage | Gases and volatiles are not RO claims |
If the result is a taste, smell or scale complaint rather than a health-effect contaminant, none of these claims is the fix: the hard water guide covers scale.
Before you buy anything
Do not buy an RO system on the strength of “removes 99 percent of contaminants” on a box. Get a lab result first, because the well and city test kit review costs less than one wrong membrane, and then match each contaminant on the report to a named claim in the unit’s own NSF listing. If you already have the report and the contaminants are in the table above, the under-sink RO review and the tankless RO review compare units by their published listings. If the report says coliform, close both and read the UV review instead.
Does softened water into an RO leave sodium behind?
This question comes up often, and the answer from Express Water’s page on pairing the two is yes, feed softened water. The softener swaps calcium and magnesium for sodium, the membrane removes 98 percent of the sodium the softener adds, and hard water above 7 grains per gallon shortens membrane life without a softener first.
Express Water sells RO systems, so the 98 percent is a vendor figure; no regulator or extension service publishes a sodium-specific rejection rate, and this page will not invent one. What the sodium does to product-water taste and pH is the remineralization guide’s job.
What should you do first?
- Get a lab report, not a strip: the table above only works against a number per contaminant.
- Compare each result with the EPA figure in the table; a result below the MCL or action level needs no claim at all.
- Open the candidate unit’s NSF listing and find each contaminant named; a missing name means no claim.
- If coliform is present, buy the NSF/ANSI 55 Class A UV stage first and come back to RO later.
- Put every replacement date for the carbon pre-filters in a calendar; they are what handle chloramine and VOCs.
Frequently asked questions
Does reverse osmosis remove PFAS?
Only when the specific unit is certified with PFOA or PFOS named in its listing. The Pennsylvania DEP list of certified point-of-use devices states that the current NSF/ANSI 53 acceptance level is 20 ppt for PFOA and 20 ppt for PFOS, with the combination not exceeding that total. NSF's fact sheet on NSF/ANSI 58 does not name PFAS among the standard's common optional claims, so read the unit's own listing.
Does reverse osmosis remove bacteria?
No NSF/ANSI 58 claim covers bacteria, viruses or cysts other than the optional cyst reduction claim. Disinfection is NSF/ANSI 55: Fresh Water Systems' summary of the standard puts Class A at a 40 mJ/cm² ultraviolet dose at highest achievable flow, rated for bacteria, viruses, Cryptosporidium and Giardia, and Class B at 16 mJ/cm² for nuisance organisms only. A coliform-positive well needs the UV stage, not an RO purchase.
Does reverse osmosis remove arsenic?
Arsenic reduction is one of the optional NSF/ANSI 58 claims listed in NSF's fact sheet on the standard, and EPA's MCL for arsenic is 0.010 mg/L. The claim is written for arsenic V; arsenic III is a different species and the arsenic-in-well-water guide on this site explains why the water may need oxidation first. A lab speciation result decides which case you have.
Does reverse osmosis remove radon or chloramine?
Not reliably. EPA's overview of drinking water treatment technologies credits reverse osmosis with inorganics, dissolved solids, radionuclides and synthetic organic chemicals, and credits granular activated carbon, not RO, with up to 99.9 percent removal of many VOCs. Dissolved gases such as radon and chloramine are handled by aeration or a carbon stage ahead of the membrane, and EPA has no enforceable MCL for radon in water.
Is softened water fine to feed into a reverse osmosis system?
Yes, per one manufacturer. Express Water's page on pairing the two states that a softener swaps calcium and magnesium for sodium, that the RO membrane removes 98 percent of the sodium the softener adds, and that hard water above 7 grains per gallon shortens membrane life without a softener first. No regulator publishes a sodium-specific rejection figure, so 98 percent stands as a vendor claim.
Fact sheet and how to cite this page
- Answer
- A reverse osmosis system removes a contaminant only when its NSF/ANSI 58 or NSF/ANSI 53 listing names that contaminant. Lead is tested at 150 ppb and must leave 5 ppb or less; PFOA and PFOS pass at 20 ppt each under NSF/ANSI 53. Bacteria is not an RO claim: NSF/ANSI 55 Class A UV at 40 mJ/cm² covers it, and dissolved gases such as radon, chloramine and VOCs need a carbon stage.
- Basis
- NSF/ANSI 58 scope per NSF’s fact sheet on the standard (TDS reduction plus optional cyst, chromium, arsenic, nitrate/nitrite, cadmium and lead claims); NSF/ANSI 53 PFOA/PFOS acceptance level per the Pennsylvania DEP certified-device list; EPA National Primary Drinking Water Regulations for the MCLs.
- Assumptions
- The unit in question carries a certified listing for the named contaminant; an uncertified RO membrane has no published pass level to hold it to
- Feed water is within the maker’s published limits and the pre-filters are in date
- Test challenge and pass levels are the standard’s laboratory conditions, not a figure for any one house
- Method
- Standards, challenge levels and MCLs read from EPA, NSF, Pennsylvania DEP and NSF certified-listing pages on 2026-09-14; where a source publishes no number, the table says so. Nothing was tested.
- Primary source
- NSF International, NSF/ANSI 58: Reverse Osmosis Drinking Water Treatment Systems (fact sheet) (manufacturer or vendor document)
- Facts verified
- Last updated
- Cite as
- OwnerSpec, "Does reverse osmosis remove PFAS, fluoride, lead, nitrate, arsenic, bacteria, microplastics and sodium? One table, by NSF/ANSI claim", https://ownerspec.com/water/guides/does-reverse-osmosis-remove-contaminant-table/, facts verified 14 September 2026.
Every figure above also appears, with its source, in the article. All sources · How OwnerSpec verifies numbers
Sources
- EPA, National Primary Drinking Water Regulations (government or regulatory source)
- EPA (archive), Radon in Drinking Water: Questions and Answers (government or regulatory source)
- EPA, Overview of Drinking Water Treatment Technologies (government or regulatory source)
- Pennsylvania DEP, Point of Use Units that are ANSI/NSF 53 Certified for the Reduction of PFOA and PFOS (PDF, updated August 2026) (government or regulatory source)
- NSF International, NSF/ANSI 58: Reverse Osmosis Drinking Water Treatment Systems (fact sheet) (manufacturer or vendor document)
- NSF, Certified Product Listings, NSF/ANSI 58 Nitrate/Nitrite Reduction (standards or certification body)
- NSF, Certified Product Listings, NSF/ANSI 58 Fluoride Reduction (standards or certification body)
- Fresh Water Systems, UV Water Purification Systems: NSF Class A and Class B (manufacturer or vendor document)
- Wastewater Digest, Maximum Allowable Lead Level Lowered to 5 ppb for NSF Certification (manufacturer or vendor document)
- PR Newswire, Coway Water Purifiers Certified for Microplastic Removal (NSF/ANSI 42 Class 1 surrogate protocol) (manufacturer or vendor document)
- Express Water, Water Softeners and Reverse Osmosis Systems (manufacturer or vendor document)