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NSF/ANSI 58: Reverse osmosis systems

Official title: Reverse Osmosis Drinking Water Treatment Systems

Covers point-of-use reverse osmosis (RO) systems. Every certified system must reduce total dissolved solids (TDS). Other claims, like lead or nitrate, are optional and listed per product.

What it can cover

  • Total dissolved solids, required for every system (listing claim: "TDS Reduction")
  • Lead and copper (listing claims: "Lead Reduction", "Copper Reduction")
  • Nitrate and nitrite (listing claim: "Nitrate/Nitrite Reduction")
  • Fluoride (listing claim: "Fluoride Reduction")
  • Pentavalent arsenic at 50 or 300 ppb or less
  • Hexavalent and trivalent chromium
  • Barium, cadmium, selenium and radium 226/228
  • Cysts and turbidity
  • Trihalomethanes (TTHM), VOCs, asbestos and perchlorate
  • PFOA and PFOS, on some WQA listings
  • Uranium, on some WQA listings

What it does not

  • Bacteria and viruses. NSF/ANSI 58 has a cyst claim but no bacteria or virus claim.
  • Chlorine taste and odor, unless the system also holds an NSF/ANSI 42 claim
  • HFPO-DA (GenX). No NSF or WQA listing shows a claim for it.
  • Lithium. No NSF or WQA listing shows a claim for it.

The usual mistake

Assuming every RO system removes everything RO can remove. Only TDS reduction is required. Lead, nitrate, arsenic and PFAS are separate claims that a given system may or may not hold.

The fine print

  • NSF says the P473 PFOA/PFOS claims were added to both 53 and 58.
  • But NSF's own 58 claims page lists no PFAS claim, and its listing search found no 58 PFAS claims on Oct. 4, 2026.
  • NSF lists RO systems' PFOA/PFOS claims under NSF/ANSI 53 instead.
  • WQA does list "Perfluorooctanoic Acid (PFOA)" and "Perfluorooctane Sulfonate (PFOS)" claims under 58.
  • Arsenic claims cover pentavalent arsenic only.
  • Listings say they fit only water at or below the stated level and valence.
  • A WQA Gold Seal listing to NSF/ANSI 58 is a real certification.
  • EPA names five ANSI-accredited certifiers that test filters to these standards: CSA Group, IAPMO R&T, NSF, UL Solutions and WQA.
  • A listing from any of them is a real certification.
  • WQA says its own accreditation comes from ANAB and SCC.

Claims to look for

ContaminantClaim on the listing
Lead
  • Lead Reduction
  • Reverse osmosis systems. WQA lists it as "Lead."
Copper
  • Copper Reduction
  • Reverse osmosis systems. WQA lists it as "Copper."
PFOA
  • Perfluorooctanoic Acid (PFOA)
  • WQA listing wording for reverse osmosis systems. NSF's own listings show no PFAS claims under 58.
PFOS
  • Perfluorooctane Sulfonate (PFOS)
  • WQA listing wording for reverse osmosis systems. NSF's own listings show no PFAS claims under 58.
Nitrate
  • Nitrate/Nitrite Reduction
  • NSF listing wording. WQA lists "Nitrate" and "Nitrite" as separate claims. NSF lists no nitrate claim under 53.
Arsenic
  • Arsenic (Pentavalent)<=50 ppb ReductionSame claim, other certifiers’ wording: Arsenic (Pentavalent)<=300 ppb Reduction
  • Pentavalent arsenic only. NSF listings say the product fits only water at or below the stated level and valence. WQA wording: "Arsenic (V) (50 ppb influent level)."
  • Same valence limit, for water up to 300 ppb. WQA wording: "Arsenic (V) (300 ppb influent level)."
Uranium
  • Uranium
  • WQA listing wording for reverse osmosis systems. NSF's listing search has no uranium claim.
Chromium (total)
  • Chromium (Hexavalent) ReductionSame claim, other certifiers’ wording: Chromium (Trivalent) Reduction
  • NSF listing wording. WQA wording: "Hexavalent Chromium."
  • NSF listing wording. WQA wording: "Trivalent Chromium."
Fluoride
  • Fluoride Reduction
  • NSF listing wording for reverse osmosis systems. WQA wording: "Fluoride."
Total trihalomethanes (TTHM)
  • Trihalomethanes (TTHM) Reduction
  • NSF listing wording for reverse osmosis systems.

Filters TapBuff has checked against a listing

Every certification below links to the certifier’s own listing. A filter appears here only if its listing shows NSF/ANSI 58.

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Sources

  1. NSF Standards for Water Treatment Systems, NSF. Checked Oct. 4, 2026.
  2. NSF/ANSI 58: Reverse Osmosis Drinking Water Treatment Systems, NSF. Checked Oct. 4, 2026.
  3. Search for NSF Certified Drinking Water Treatment Units (standards and reduction claims lists), NSF. Checked Oct. 4, 2026.
  4. NSF listings search for NSF/ANSI 58 PFOA, PFOS and Total PFAS claims (no matching products), NSF. Checked Oct. 4, 2026.
  5. NSF listings for the NSF/ANSI 58 pentavalent arsenic claim (valence footnote), NSF. Checked Oct. 4, 2026.
  6. Contaminant Reduction Claims Guide, NSF. Checked Oct. 4, 2026.
  7. Forever Chemicals and the Advancement of Filtration Standards, NSF. Checked Oct. 4, 2026.
  8. Water Filters FAQs, NSF. Checked Oct. 4, 2026.
  9. Find WQA Certified Products (Gold Seal listings by standard and claim), Water Quality Association. Checked Oct. 4, 2026.
  10. Product Certification, Water Quality Association. Checked Oct. 4, 2026.
  11. Fact Sheet: Reducing PFAS in Your Drinking Water with a Home Filter (April 2024), U.S. EPA. Checked Oct. 4, 2026.