NSF/ANSI 42, 53, and 401 Explained
Reviewed by FiltersDex editorial
NSF/ANSI 42, 53, and 401 are three separate certification standards for water filters, each covering a different category of contaminant - a filter certified under one is not automatically certified under the others.
NSF International and ANSI publish standards that filter manufacturers pay to be independently tested against. Passing means the filter reduces a specific, published list of contaminants by a required amount under lab conditions - it is not a self-declared marketing claim.
NSF/ANSI 42 - taste and odor (aesthetic)
Covers aesthetic effects: chlorine taste and odor, mainly. This is the baseline certification nearly every basic filter should meet, but it says nothing about health contaminants like lead.
NSF/ANSI 53 - health contaminants
Covers substances with a health effect: lead, cysts (like Cryptosporidium and Giardia), mercury, and others, depending on which specific claims the filter was tested and certified for. A filter can be 53-certified for some of these and not others - check the exact contaminant list, not just the standard number.
NSF/ANSI 401 - emerging compounds
A newer standard covering trace "emerging" compounds not covered by 42 or 53 - certain pharmaceuticals, BPA, and similar substances found in small concentrations in some water supplies.
See exactly which standard and which contaminants each filter we cover is certified for on its filter page, or browse by what your filter removes.
Frequently asked
Is NSF/ANSI 53 better than NSF/ANSI 42?
They test different things, so "better" depends on what you want removed. 42 covers aesthetic issues like chlorine taste; 53 covers health-related contaminants like lead and cysts.
Does NSF/ANSI 401 cover everything 42 and 53 don't?
No. NSF/ANSI 401 covers a specific list of "emerging" compounds like certain pharmaceuticals and BPA - it is a separate, additional certification, not a catch-all.
Can a filter be certified under more than one standard?
Yes, and most higher-end filters are - a filter can carry 42, 53, and 401 certifications at once, each covering different contaminants, listed separately.
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