What does the NSF / ANSI certification mean on a water filter?

What does the NSF / ANSI certification mean on a water filter?

Product Listings and Certifications by NSF International (formerly, National Sanitation Foundation) are easily confused, and this article is to help you understand NSF certifications and listings.

NSF is a not-for-profit corporation founded in 1944 to promote good sanitation. Its main "business" is to bring together experts in public health, manufacturing, and sanitation from government, industry, academia and the public to develop and administer performance standards for products which have some impact on sanitation and public health. NSF maintains state-of-the-art laboratories where products can be tested according to the standards.

Manufacturers voluntarily submit products for evaluation; if they pass the tests, they are "Listed" and certain tested claims are "Certified," and the products are authorized to display the NSF Seal on labels and literature. Although non-governmental, NSF does have some official status as the lead agency for the testing and approval of both the chemicals used in water treatment and the materials of construction used in drinking water systems, under contract to the U.S. Environmental Protection
Agency. NSF Standards are recognized by the American National Standards Institute (ANSI) and the equivalent organization in the European Community, the Dutch Council for Certification (RvC). Public Health Officials worldwide can take confidence from the knowledge that people like themselves have written and approved these standards, and NSF's reputation for thoroughness, independence and credibility has made it one of the most trusted public agencies in the world. NSF has also received the distinction of being appointed a Registrar for the International Standards Organization (ISO) and a World Health Organisation (WHO) Collaborating Center for Water Safety and Treatment.

There are two NSF Standards for "Drinking Water Treatment Units" (not including others for reverse osmosis, ion exchange, and ultra-violet units): Standard 42 for Aesthetic Effects, and Standard 53 for Health Effects. They are similar, and most of the basic requirements are the same for both. A water filter which is "NSF-Listed:' or which has claims which are "NSF-Certified" is one which:

1. is thoughtfully designed and carefully constructed
a) using established water treatment media and methods,
b) using materials of construction which are tested and documented to be appropriate for potable water use,
c) and is tested and verified to conform to minimum standards of mechanical and hydraulic strength,
d) and is tested and verified to conform to minimum standards of hydraulic functioning (minimum flow rate, maximum initial pressure drop, reasonable freedom from channeling and dumping),
2. is adequately and truthfully labeled and advertised,
3. is routinely re-tested, and its manufacturing procedures, documentation and facilities inspected/audited annually, and 4. in addition to the above "good manufacturing practices" required of all Listed products, has been tested and approved for one or more specific functions which are required to be listed immediately next to the NSF Seal on labels and literature.

Standard 42 claims for general mechanical filtration and chlorine / taste odor reduction have classes of performance, but for all other claims there is only a pass/fail.

For Taste & Odor, the classes represent chlorine reduction efficiency:
Class I, a minimum of 75% chlorine reduction
Class II, 50% reduction
Class III, 25%.

For mechanical filtration, the classes represent particle size ranges which are removed with a minimum 85% efficiency:
Class I, ½ -1 micron
Class II, 1-5 microns
Class III, 5-15 microns
Class IV, 15-30
Class V, 30-50
Class VI, 50+ microns.

Note that a Class I or II rating does not imply Cyst Reduction-that requires a 99.95% minimum filtration efficiency for 3-4 micron test dust particles, 3.000 micron micro-spheres, or live  cryptosporidium oocysts.