Have you ever wondered what the ‘NSF’ acronym means on the packaging or websites of some water treatment products? Or, better yet, what it means when those three letters aren’t there? We’ll go over the basics so you not only understand that designation, but are able to make more informed choices when you’re shopping around for water treatment products.

The National Sanitation Foundation (NSF) is an independent product testing, inspection, and certification organization.

Note: This NSF is not to be confused with the National Science Foundation.

One of the many functions of the NSF is to conduct testing and certification of water treatment devices to ensure that the devices are composed of nontoxic materials and/or that they reliably and adequately remove certain contaminants.

Federal agencies that regulate drinking water (i.e. the EPA and FDA) do not regulate treatment devices, so certifications aim to provide unbiased information to help consumers decide which products will be effective for their water treatment needs. Some of the most popular NSF certifications address materials safety, structural integrity and specific contaminant reduction claims.

In addition to the NSF, there are a couple of other relevant agencies that also certify water treatment products, often in conjunction with the NSF.

The American National Standards Institute (ANSI) is a US-based non-profit organization that manages the development of voluntary consensus standards for products, services, techniques, systems, and personnel. ANSI helps establish national standards and identify gaps in conformity assessment activities. Another major role of ANSI is to accredit the organizations that uphold industry standards, including certification labs, inspection bodies, personnel credentialing bodies, and other conformity assessment structures used to hold people and industries accountable. In conjunction with the National Sanitation Foundation, ANSI has developed a multitude of standards for at-home water treatment products.

The Water Quality Association (WQA) is an organization that conducts research, education, and product testing and certification for the water treatment industry. The WQA tests drinking water treatment system components, water additives, pool and spa equipment, and food equipment that involves potable water. The agency provides the WQA Gold Seal Certification to products that have undergone testing in WQA's lab or other certified labs, and meet quality standards established by the NSF and ANSI. WQA tests and certifies products for safe materials, removal claims by manufacturers, and sustainability. WQA certifications are useful for consumers when considering which products will be effective for their needs.

In the context of home water treatment products, ‘certification’ means that the product has performed to the standards that are specified in the specific certifications. Essentially, the product has passed the test that the agency designed. These tests are typically called ‘challenge tests’ and involve adding a specific amount of a contaminant to water and determining how much of that contaminant the product removes, then comparing that removal with the amount of removal specified in the standard. The certifications that we are focused on here are developed jointly by the NSF and ANSI and are referred to as NSF/ANSI, followed by a number. The WQA uses the NSF/ANSI standards for its own certification so we’ll be discussing NSF/ANSI certifications only.

When it comes to NSF/ANSI certifications, there are a couple of points that apply to all certifications:

Here is a quick run down of some of the most relevant certifications when it comes to home water treatment devices.

The NSF/ANSI 42 standard is used to certify products for removing or reducing concentrations of contaminants that may cause negative aesthetic effects (i.e. color, taste and odor impacts). The standard establishes minimum requirements for removing or reducing the concentrations of compounds that cause an unpleasant taste, odor or color in drinking water, including aesthetic chlorine, chloramines, sizable particulates and microbes, manganese, iron, and zinc. NSF/ANSI 42 certification is used for both point of use (i.e. under the sink and pitcher filters) and point of entry systems.

The NSF/ANSI 53 standard is used to certify water treatment products for removing or reducing concentrations of contaminants that have the potential to cause health problems. The standard establishes minimum removal requirements for specific health-related contaminants. Some of the contaminants included in this certification are lead, asbestos, volatile organic compounds, Cryptosporidium, perfluoroalkyl substances (PFAS), and chromium. NSF/ANSI 53 certification is used for both point of use (i.e. under the sink and pitcher filters) and point of entry systems.

The NSF/ANSI 401 standard is used to certify water treatment products for removing or reducing concentrations of contaminants that have effects that are not fully researched (i.e., ‘contaminants of emerging concern’). The NSF established this certification due to increasing consumer concerns about potential effects from exposure to various emerging contaminants via drinking water. The standard establishes minimum requirements for the removal or reduction of certain emerging contaminants of concern, including a number of pharmaceuticals and pesticides. NSF/ANSI 401 certification is used for both point of use (i.e. under the sink and pitcher filters) and point of entry systems.

The NSF/ANSI 58 standard is used to certify point of use (e.g. under the sink) water treatment systems employing reverse osmosis, a high-pressure filter technology designed to remove a wide array of contaminants of concern. NSF/ANSI 58 establishes minimum requirements for total dissolved solids (TDS) reduction and contaminant removal or reduction. Some of the contaminants included in this certification are nitrate, lead, arsenic, volatile organic compounds,

The NSF/ANSI 44 standard is used to certify cation exchange water softeners for residential use. Water softening products covered by NSF/ANSI 44 reduce hardness by replacing calcium and magnesium with sodium or potassium. The standard establishes minimum requirements for the softening capacity and regenerated salt concentration of the products. It also dictates minimum removals for hardness minerals and certain other cations, including barium and radium. The NSF/ANSI 44 certification is used for both point of use (i.e. under the sink) and point of entry water softening systems.

The NSF/ANSI 55 standard is used to certify ultraviolet disinfection treatment systems designed to deactivate bacteria, protozoa, and viruses. The standard establishes requirements for the disinfection performance, material performance, and labeling information for certified products. There are two UV water treatment system classifications covered under this standard, Class A and Class B. Class A products have been tested and certified to reduce prevalent protozoa resistant to typical chlorine disinfection, including cryptosporidium and giardia, as well as bacteria and viruses to safe levels. Class B products have been tested and certified to further reduce microbe concentrations in water that is already deemed safe by health agencies. Class B certified products should not be used in the case of known harmful microbial contamination. The NSF/ANSI 55 certification is used for both point of use (i.e. under the sink) and point of entry UV systems. Even Class A certified products are not recommended for cloudy, turbid water or water with a clear source of contamination. For example, these products should not be used to convert sewage wastewater to drinking water.

The NSF/ANSI 177 standard is used to certify point of use shower filters. Some studies suggest that elevated levels of chlorine in tap water left over from disinfection processes can dry out the skin and damage hair. NSF/ANSI 177 certified shower filters are certified for labeling information and the reduction of free available chlorine.

The NSF/ANSI 62 standard is used to certify distillation water treatment systems for residential use. Distillation systems heat water to its boiling point and collect the evaporated water, leaving behind most harmful contaminants. NSF/ANSI 62 establishes requirements for TDS reduction and the reduction of additional contaminants, including arsenic, chromium, mercury, nitrate, nitrite, bacteria, and protozoan cysts. The NSF/ANSI 62 certification is used for both point of use (i.e. under the sink) and point of entry distillation systems.

*UV products are not recommended for use with cloudy, turbid water or water with a clear source of contamination

The short answer: not necessarily. Many uncertified products reduce contaminants to the same degree as their certified counterparts, it’s just hard to know if the manufacturer claims of contaminant reduction are accurate without third party testing. The reason that some companies don’t get their products certified is that the testing and certification can be expensive so some companies choose not to certify even if the products would pass. In the end, NSF certifications give credence to manufacturer claims regarding contaminant reduction. Without certifications, you’ll need to look more deeply into the product and perhaps even test the treated water yourself.