Water Filter Certifications Explained: NSF 42, 53, 58, P473
What NSF and ANSI certifications mean and which ones matter.
NSF/ANSI 42: Aesthetic
Tests for chlorine taste and odor, particulates. The most basic certification. Nearly all carbon filters achieve this. It does NOT mean the filter removes contaminants like lead or PFAS.
NSF/ANSI 53: Health Effects
Tests for specific contaminants that affect health: lead, VOCs, cysts (Giardia, Cryptosporidium), mercury, MTBE, and more. This is the certification that matters for safety. Look for the specific contaminants listed on the certification, not just "NSF 53."
NSF/ANSI 58: Reverse Osmosis
Tests the complete RO system including TDS reduction, individual contaminant removal, and system efficiency. All quality RO systems should have this.
NSF P473: PFAS
The only standard specifically testing for PFAS (PFOS and PFOA) removal. Relatively new. Not all filters marketed for PFAS have this certification. See our PFAS filter guide.
NSF 401: Emerging Contaminants
Tests for pharmaceuticals, BPA, pesticides, and herbicides. Newer standard, fewer products certified.