What do NSF/ANSI 42, 53, 58, 401 and 473 mean?
NSF/ANSI 42: certifies that point-of-use or whole-house filters reduce non-health (aesthetic) contaminants such as chlorine, taste and odor, chloramine, particulate, iron, manganese, zinc and TDS; NSF/ANSI 53: certifies that point-of-use or whole-house filters reduce specific health-related contaminants (over 50 claims, e.g., lead, Cryptosporidium, VOCs, chromium, PFOA/PFOS); NSF/ANSI 58: covers reverse osmosis systems that push water through a semi-permeable membrane to reduce EPA/Health Canada-regulated contaminants; NSF/ANSI 401: certifies reduction of up to 15 trace 'emerging' contaminants (e.g., certain pharmaceuticals, herbicides, pesticides, BPA) not regulated by EPA/Health Canada; microplastics claim also sits here; NSF/ANSI 473: NSF P473 was a 2016 protocol testing filter reduction of PFOA/PFOS to EPA's 2016 70 ppt health advisory; its methods were folded into NSF/ANSI 53 and 58, and all P473 listings were replaced by 53/58. A product is certified only if a certifier lists it; "tested to NSF standards" is not a certification.
The standards
| Standard | What it covers |
|---|---|
| NSF/ANSI 42 | Certifies that point-of-use or whole-house filters reduce non-health (aesthetic) contaminants such as chlorine, taste and odor, chloramine, particulate, iron, manganese, zinc and TDS. |
| NSF/ANSI 53 | Certifies that point-of-use or whole-house filters reduce specific health-related contaminants (over 50 claims, e.g., lead, Cryptosporidium, VOCs, chromium, PFOA/PFOS). |
| NSF/ANSI 44 | Covers water softeners that swap calcium and magnesium (hardness) for sodium or potassium. |
| NSF/ANSI 55 | Covers UV systems: Class A inactivate bacteria, viruses and cysts in contaminated water; Class B reduce non-disease-causing bacteria in already-disinfected water. |
| NSF/ANSI 58 | Covers reverse osmosis systems that push water through a semi-permeable membrane to reduce EPA/Health Canada-regulated contaminants. |
| NSF/ANSI 62 | Covers distillers that boil water and collect the condensed vapor, leaving contaminants such as heavy metals behind (some VOCs can carry over). |
| NSF/ANSI 177 | Covers shower filters, which are certified only to reduce free available chlorine. |
| NSF/ANSI 244 | Covers filters for already-treated public water that protect against intermittent microbiological contamination (bacteria, virus and cyst claims); not for untreated water. |
| NSF/ANSI P231 | NSF protocol certifying 'microbiological water purifiers' based on EPA's 1987 Guide Standard and Protocol for Testing Microbiological Water Purifiers. |
| NSF/ANSI 401 | Certifies reduction of up to 15 trace 'emerging' contaminants (e.g., certain pharmaceuticals, herbicides, pesticides, BPA) not regulated by EPA/Health Canada; microplastics claim also sits here. |
| NSF/ANSI 473 | NSF P473 was a 2016 protocol testing filter reduction of PFOA/PFOS to EPA's 2016 70 ppt health advisory; its methods were folded into NSF/ANSI 53 and 58, and all P473 listings were replaced by 53/58. |
| NSF/ANSI 61 | Covers pipes, fittings, faucets and other components that touch drinking water, limiting chemicals they leach into it; required by state plumbing codes, not a filter-performance standard. |
| NSF/ANSI 372 | Verifies plumbing products meet the federal 'lead free' definition: weighted average of no more than 0.25% lead on wetted surfaces (0.2% for solder and flux). |
How to check a listing
Sources
- NSF/ANSI 42: Drinking Water Treatment Units - Aesthetic Effects
- NSF/ANSI 53: Drinking Water Treatment Units - Health Effects
- NSF/ANSI 44: Residential Cation Exchange Water Softeners
- NSF/ANSI 55: Ultraviolet Microbiological Water Treatment Systems
- NSF/ANSI 58: Reverse Osmosis Drinking Water Treatment Systems
- NSF/ANSI 62: Drinking Water Distillation Systems
- NSF/ANSI 177: Shower Filtration Systems - Aesthetic Effects
- NSF/ANSI 244: Supplemental Microbiological Water Treatment Systems
- NSF/ANSI P231: Microbiological Water Purifiers (protocol)
- NSF/ANSI 401: Emerging Compounds / Incidental Contaminants
- NSF/ANSI 473: PFOA/PFOS reduction (protocol, retired)
- NSF/ANSI 61: Drinking Water System Components - Health Effects
- NSF/ANSI 372: Drinking Water System Components - Lead Content
Last checked 2026-10-23.