NSF Standards for Water Treatment Systems

While no federal regulations exist for residential water treatment filters, purifiers and reverse osmosis systems, voluntary national standards and NSF International protocols have been developed that establish minimum requirements for the safety and performance of these products to treat drinking water. The standards and protocols are explained in detail below. The numbers in the names reflect the order in which the standard or protocol was developed and are not a ranking or rating system.

  • NSF/ANSI 42
    Filters are certified to reduce aesthetic impurities such as chlorine and taste/odor. These can be point-of-use (under the sink, water pitcher, etc.) or point-of-entry (whole house) treatment systems.
  • NSF/ANSI 53
    Filters are certified to reduce a contaminant with a health effect. Health effects are set in this standard as regulated by the U.S. Environmental Protection Agency (EPA) and Health Canada. Both standards 42 and 53 cover adsorption/filtration which is a process that occurs when liquid, gas or dissolved/suspended matter adheres to the surface of, or in the pores of, an adsorbent media. Carbon filters are an example of this type of product.
  • NSF/ANSI 44
    Water softeners use a cation exchange resin that is regenerated with sodium or potassium chloride. The softener reduces hardness caused by calcium and magnesium ions and replaces them with sodium or potassium ions.
  • NSF/ANSI 55
    Ultraviolet treatment systems use ultraviolet light to inactivate or kill bacteria, viruses and cysts in contaminated water (Class A systems) or to reduce the amount of non-disease causing bacteria in disinfected drinking water (Class B).
  • NSF/ANSI 58
    Reverse osmosis systems incorporate a process that uses reverse pressure to force water through a semi-permeable membrane. Most reverse osmosis systems incorporate one or more additional filters on either side of the membrane. These systems reduce contaminants that are regulated by Health Canada and EPA.
  • NSF/ANSI 62
    Distillation systems heat water to the boiling point, and then collect the water vapor as it condenses, leaving behind contaminants such as heavy metals. Some contaminants that convert readily into gases, such as volatile organic chemicals, can carry over with the water vapor.
  • NSF/ANSI 177
    Shower filters attach directly to the pipe just in front of the homeowner’s showerhead and are certified to only reduce free available chlorine.
  • NSF/ANSI 401
    Treatment systems for emerging contaminants include both point-of-use and point-of-entry systems that have been verified to reduce one or more of 15 emerging contaminants from drinking water. These emerging contaminants can be pharmaceuticals or chemicals not yet regulated by the EPA or Health Canada.
  • NSF P477
    These point-of-use filters reduce microcystin (toxins produced by blue-green algae) below the health advisory set by the EPA.
  • NSF P473
    PFOA/PFOS water filters or systems are evaluated on their ability to reduce PFOA and PFOS in drinking water and to meet strict material safety and structural requirements as defined in NSF/ANSI 53.
  • NSF P231
    Microbiological water purifiers are certified for health and sanitation based on the recommendations of the EPA’s Task Force Report, Guide Standard and Protocol for Testing Microbiological Water Purifiers (1987) (Annex B).
  • NSF/JWPA P72
    Iodine radioisotope point-of-use treatment options are evaluated for reduction of all forms of iodine in drinking water. This protocol was developed in conjunction with the Japan Water Purifier Association (JWPA).

Keep in mind that certification to an NSF/ANSI standard or protocol does not mean that a filter, purifier or treatment system will reduce all possible contaminants. It’s important to verify that the filter, purifier or treatment system is certified to the applicable standard for the reduction of the contaminants of most concern to you or your family. Review our step-by-step guide on selecting home water treatment systems for more information.

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