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 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 244
  The filters covered by this standard are intended for use only on public water supplies that have been treated or that are determined to be microbiologically safe. These filters are only intended for protection against intermittent microbiological contamination of otherwise safe drinking water. For example, prior to the issuance of a boil water advisory, you can be assured that your filtration system is protecting you from intermittent microbiological contamination. The standard also includes material safety and structural integrity, similar to other NSF/ANSI drinking water treatment unit standards. Manufacturers can claim bacteria, viruses and cysts reduction for their filtration system.
• 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 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).

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.