Standards for Water Treatment Systems

While no federal regulations exist for residential water treatment devices, several voluntary national standards establish minimum requirements for the safety and performance of products used to treat home drinking water. These standards are generally divided according to the product’s technology. The numbers assigned to each standard reflect the order in which the standards were developed.

Below are the standards and the type of technology each covers, along with a description of the purpose or intended function of the technology.

  • Adsorption/Filtration (NSF/ANSI 42 & 53)
    This process occurs when liquid, gas or dissolved or 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.
  • Softeners (NSF/ANSI 44)
    These systems incorporate a cation exchange resin that is regenerated with sodium or potassium chloride. The softener reduces calcium and magnesium ions and replaces them with sodium or potassium ions.
  • Ultraviolet Treatment (NSF/ANSI 55)
    These systems use ultraviolet light to disinfect water (Class A systems) or to reduce the amount of non-disease causing bacteria in water (Class B).
  • Reverse Osmosis (NSF/ANSI 58)
    These 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.
  • Distillers (NSF/ANSI 62)
    These 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.
  • Shower Filters (NSF/ANSI 177)
    These products attach directly to the pipe just in front of the homeowner’s showerhead.
  • Treatment Systems for Emerging Contaminants (NSF/ANSI 401)
    Systems covered by this standard include several types of point-of-use (POU) and point-of-entry (POE) systems that have been verified to reduce up to 15 emerging contaminants from drinking water.

Keep in mind that certification to an NSF/ANSI standard does not mean that a product is able to effectively reduce all possible contaminants. It’s important to verify that the product is certified under that standard for reduction of the specific impurities of most concern to you or your family.