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

Product listings and certifications by the National Sanitation Foundation International (NSF International) are easily confused, which is why we thought it might be beneficial to explain how water filters earn this certification. We want to help you understand what it means when a water filter has NSF certifications and listings on it.

NSF LogoNSF International is a not-for-profit corporation that was founded in 1944 to promote good sanitation. Its main goal is to bring together experts in public health, manufacturing, and sanitation. These experts come from government, industry, academia and public background to develop and administer performance standards for products that have some impact on sanitation and public health. NSF maintains state-of-the-art laboratories where products can be tested according to the standards they establish.

Manufacturers voluntarily submit products for evaluation. If they pass the tests, then they are “listed” and certain tested claims are “certified.” These products are now authorized to display the NSF/ANSI seal on their labels and literature. Although non-governmental, NSF International does have some official status as the lead agency for testing and approving the chemicals used in water treatment plants and the materials of construction used in drinking water systems. This status is due to their contract with the U.S. Environmental Protection Agency.

NSF International standards are recognized by the American National Standards Institute (ANSI) and the Dutch Council for Certification (RVC), which is the equivalent organization in the European Community. The ANSI is a private, nonprofit corporation that was founded in 1918. The goal of ANSI is to help enhance the “global competitiveness of U.S. business and the American quality of life by promoting and facilitating voluntary consensus standards.”

NSF International’s reputation for thoroughness, independence and credibility has made it one of the most trusted public agencies in the world. This well-known corporation has also received the distinction of being appointed a registrar for the International Standards Organization (ISO) and a World Health Organization (WHO) Collaborating Center for Water Safety and Treatment.

There are two NSF International/ANSI 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. These standards are similar and most of the basic requirements are the same for both. A water filter that is “NSF-Listed’ or has claims that it is “NSF-Certified” basically means:

  1. It’s been thoughtfully designed and carefully constructed.
  • Uses established water treatment media and methods.
  • Its construction materials are tested and documented to be appropriate for potable water use.
  • The filter is tested and verified to conform to minimum standards of mechanical and hydraulic strength.
  • It is also tested and verified to conform to minimum standards of hydraulic functioning (minimum flow rate, maximum initial pressure drop, reasonable freedom from channeling and dumping).
  1. Adequately and truthfully labeled and advertised.
  2. Routinely re-tested. Its manufacturing procedures, documentation and facilities are inspected and audited annually.

  3. In addition to the above “good manufacturing practices” required of all “listed” products, it’s been tested and approved for one or more specific functions that are required to be listed immediately next to the NSF International seal on labels and literature.

NSF Logo on Water Filter

Water filters with a Standard 42 (aesthetic effects) certification are designed to minimize non-health related contaminants such as chlorine, taste and odor, and particulates. These filters sorted by classes of performance. For all other claims, there is only a pass or 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 that 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 microns.
Class V, 30-50 microns.
Class VI, 50+ microns.

It’s important to note a Class I or Class II rating does not imply cyst reduction. In order for a water filter to qualify for cyst reduction, it must have a 99.95 percent minimum filtration efficiency for 3-4 micron test dust particles, 3.000 micron micro-spheres, or live cryptosporidium oocysts.

Water filters with a Standard 53 (health effects) certification are meant to reduce health-related contaminants that may be present in public or private drinking water. Filters that meet the Standard 53 requirements are able to minimize exposure to microbiological, chemical or particulate contaminants that might be hazardous to your health. These types of filters are typically best suited for individuals who have well water.

Some filters fall under the scope of both abovementioned standards since they meet aesthetic and health related claims.

Let us know if you have any other questions concerning the difference between NSF/ANSI certifications on water filters! Check out our article about U.S. Regulations on Drinking Water to learn more about the importance of safe drinking water.

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

  1. Tom

    While NSF can be a great standard to follow, they are in no way a not-or-profit organization. For example, for a product to get tested to be able to have NSF certification, it will cost about $100,000, just for testing, which can be done very quickly and easily, so they are making a lot money. Secondly, there are water filters on the market that are far superior to other water filters, but because they are in the beginning stages of the company, cannot afford to get this certification, in which does that make them worse, or not good, no. And, products that are NSF certified, don’t label the class they met, and most that have the NSF 42 certification, only remove about 42% of the chlorine. And chlorine is not aesthetic, it is hazardous, so there puts a dent in the credibility of NSF, and when reacting with organic compounds, found in all water, creates carcinogenic chemicals, so it is in no way safe.

    1. Katie

      Thanks for your comments Tom!

      According the NSF website, the organization became a not-for-profit corporation in 1967 and hasn’t changed since. Just because an organization makes money does not make it unable to be a not-for-profit, take for example Universities.

      It is definitely a good point to make that non-certified filters could be just as good, if not better than certified filters.


  2. Dave

    NSF is not a standard, they do the testing. As a consumer, its ANSI 53 or no sale. Tested by NSF, UL, or other known lab. I will only buy a water filter tested and certified. I wonder about your credibility.

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