Independent certification is one of the best ways to check a dealer's claims. These are the main NSF/ANSI standards for home water treatment:
| Standard | Covers |
|---|---|
| NSF/ANSI 44 | Residential cation-exchange water softeners: material safety, structural integrity, softening capacity and related performance.1 |
| NSF/ANSI 58 | Point-of-use reverse osmosis systems: material safety, structural integrity, TDS reduction, efficiency and any specific contaminant claims.2 |
| NSF/ANSI 42 | Filters that reduce aesthetic issues like chlorine, taste and odor.3 |
| NSF/ANSI 53 | Filters that reduce specific health-related contaminants, but only the ones named in that product's listing.3 |
How to use this when shopping
- Ask for the exact model number and look it up in NSF's listings. "Uses certified components" isn't the same as a certified system.
- Check that the contaminant you care about (for example arsenic) is named in the listing.
- Compare quotes with our dealer checklist.
Sources
- NSF: NSF/ANSI 44 technical requirements
- NSF: NSF/ANSI 58 reverse osmosis systems
- NSF: NSF/ANSI 42, 53 and 401 filtration standards
Last reviewed Oct 13, 2026. This is general information, not professional advice. Confirm figures with your utility and installer.