What Is NSF/ANSI 42? The Standard for Taste and Odor

If your water is safe but tastes or smells like a swimming pool, this is the standard that matters to you. NSF/ANSI 42 covers “aesthetic effects”: things you can taste, smell or see, not contaminants that affect your health.

What does NSF/ANSI 42 certify?

On NSF’s listings for the standard, the claims that come up most are chlorine reduction and taste and odor reduction, followed by nominal particulate reduction, chloramine reduction and zinc reduction. The products range from pitchers, faucet-mount and countertop filters to under-sink units, refrigerator filters and whole-house (point-of-entry) systems.

Chlorine and chloramine are separate claims. If you know your utility disinfects with chloramine, look for that claim specifically: a listing with only a chlorine claim isn’t certified for chloramine.

Is NSF/ANSI 53 better than NSF/ANSI 42?

Neither is “better”: they certify different things. For taste and smell, 42 is the right standard. For anything health-related, it isn’t. A filter certified only to 42 hasn’t been certified to reduce lead, PFAS or other health contaminants; those claims are made under NSF/ANSI 53 (or 58 for reverse osmosis).

That’s why many good filters carry both. The EPA’s consumer tool for lead filters tells you to look for certification to NSF/ANSI 53 with a lead reduction claim, and recommends also looking for NSF/ANSI 42 particulate reduction (Class I). Wisconsin’s health department, in its guide for well owners, points to NSF/ANSI 42 only for zinc, and to 53 for contaminants such as lead, atrazine, VOCs and PFAS.

How do you check a 42 claim?

Look up the exact model and replacement cartridge in the certifier’s own listing (NSF, WQA, IAPMO and others certify to this standard) and make sure the claim you care about is listed. A filter can be certified for chlorine taste and odor without any particulate or chloramine claim.

If the taste of chlorine is your only complaint, a filter certified to 42 for chlorine, taste and odor is what you’re after; you don’t need a reverse osmosis system for that. If you’re worried about something you can’t taste, like lead, read our guide to lead in drinking water first.