Glossary · Certification and standards

What Is NSF/ANSI 177? The Shower Filter Standard

NSF/ANSI 177Shower Filtration Systems: Aesthetic Effects

The NSF/ANSI standard for shower filters; on NSF's listings, its only certified claim is free available chlorine reduction, an aesthetic effect.

  • NSF/ANSI 42Aesthetic effects: taste, odor, particlesChlorine, chloramine, taste and odor, particulates, zincPitchers, faucet, under-sink, fridge and whole-house filters
  • NSF/ANSI 53Contaminants with health effectsLead, cysts, VOCs, mercury, PFOA/PFOSPitchers, faucet, countertop, under-sink and fridge filters
  • NSF/ANSI 58Reverse osmosis drinking water systemsTDS (required); optional claims such as lead, fluoride, arsenic, nitrateReverse osmosis systems, mostly under-sink
  • NSF/ANSI 401Emerging compounds and incidental contaminantsIbuprofen, BPA, DEET, some herbicides, microplasticsPitchers, faucet, under-sink and fridge filters
  • NSF/ANSI 44Cation exchange (salt-based) water softenersHardness, salt efficiency, barium, radium 226/228Whole-house water softeners
  • NSF/ANSI 55Ultraviolet (UV) systems for microbesClass A: bacteria, viruses, cysts; Class B: nuisance microbesWhole-house and point-of-use UV systems
  • NSF/ANSI 177Shower filters, aesthetic effects onlyFree available chlorineShower filters
NSF/ANSI 177 among the drinking water standards: it is the one for shower filters.

At a glance

Official name
Shower Filtration Systems, Aesthetic Effects
Only claim listed
Free available chlorine reduction
Not covered
Hardness (softening), lead, PFAS or other health claims
Certified by
NSF and IAPMO R&T, among others

Shower filters are sometimes sold as a fix for hard water or as a way to filter out a long list of contaminants. NSF/ANSI 177 is the standard for shower filters, and it certifies something much narrower.

What does NSF/ANSI 177 certify?

The standard’s full name is “Shower Filtration Systems, Aesthetic Effects,” and on NSF’s listings for it, the only claim certified is free available chlorine reduction. As the name says, it’s about aesthetic effects, not health.

So a certified shower filter has been checked for one thing: cutting chlorine. Any other claim on the box, from softening to lead, is the maker’s.

Will a shower filter fix hard water?

No. Softening means removing calcium and magnesium, and in NSF’s listings the Hardness Reduction claim appears only under NSF/ANSI 44, the standard for cation exchange water softeners. A shower filter certified under 177 isn’t certified to remove hardness. Our hard water guide covers what actually works, and why many people decide they don’t need to treat hard water at all.

How do you check a shower filter claim?

Search the certifier’s listing for the exact model and its replacement cartridge, and confirm that “Free Available Chlorine Reduction” is listed under NSF/ANSI 177. NSF isn’t the only option: IAPMO R&T, for one, includes NSF/ANSI 177 among the standards it certifies to.

If chlorine smell in the shower is what bothers you, a filter certified under 177 is built for exactly that. If your worry is something in the water you drink, a shower filter is the wrong tool: look at filters certified under NSF/ANSI 53 for the specific contaminant instead.

Published by the Checked Water editorial team

Sources

  1. NSF Listings: NSF/ANSI 177 Shower Filtration Systems, Aesthetic Effects (Source, NSF, 2026)
  2. NSF Listings: NSF/ANSI 44 Cation Exchange Water Softeners (Source, NSF, 2026)
  3. Search for NSF Certified Drinking Water Treatment Units, Water Filters (Source, NSF, 2026)
  4. Water Systems Certification (Source, IAPMO R&T, 2026)

Where NSF/ANSI 177 comes up