Ultraviolet (UV) Water Treatment Systems, NSF/ANSI 55-2022

Water leaking from faucet nice and clean with NSF/ANSI 55-2022 UV microbiological treatment.

Of the many objectives at federal, state, and local levels, guaranteeing access to safe, clean water is an utmost necessity. However, many are faced with the presence of contaminants in their already-treated water supplies, garnering the need for further guidance to reduce microorganisms in drinking water. Reduction of microorganisms can be achieved through the use of ultraviolet radiation (UV). NSF/ANSI 55-2022, an American National Standard, addresses ultraviolet microbiological water treatment systems.

NSF/ANSI 55-2022: Ultraviolet Microbiological Water Treatment Systems

The first edition of NSF/ANSI 55 was released by NSF International with considerations discussed in the 1987 expert task force’s report, Report of Task Force on Guide Standard and Protocol for Testing Microbiological Water Purifiers, and subsequent revisions have built off that knowledge. NSF/ANSI 55-2022: Ultraviolet microbiological water treatment systems, the newest revision, covers the minimum requirements for point-of-entry and point-of-use UV water treatment systems that may be either microbiologically safe or microbiologically unsafe. These UV treatment systems are not intended for water that has an obvious contamination.

Through UV exposure from the treatment units designed in accordance with NSF/ANSI 55-2022 requirements, users can reduce a variety of microorganisms from water supplies. These bacteria and viruses can impose serious threats to public health.

For example, some of the microorganisms reduced through NSF/ANSI 55-2022 requirements include:


Cryptosporidium is a microscopic parasite that lives in the intestines of infected humans or animals, causing the disease cryptosporidiosis. Since Cryptosporidium oocysts are protected by a strong outer shell that allows them to survive outside of the body for long periods of time, they are highly tolerant to chlorine disinfection.

Millions of Crypto parasites are released in bowel movements from infected individuals, and exposed individuals can become infected after accidentally swallowing the alveolates. Due to their resistance to chlorine and their main point of infection being through consumption, cryptosporidiosis is primarily spread through drinking water and recreational water. Symptoms of cryptosporidiosis are mainly gastrointestinal in nature and are often paired with fever and weight loss. These symptoms last for about 1 to 2 weeks in persons with healthy immune systems.

In the United States, there are approximately 748,000 cases of cryptosporidiosis each year.


Giardia cysts, like Cryptosporidium, are protected from chlorine disinfection by their strong outer shell. Because of this characteristic, Giardia are also spread through drinking water and recreational water that has been contaminated with feces from infected individuals.


Giardiasis, which results from consumption of Giardia, is the most frequently diagnosed intestinal parasitic disease in the United States. The symptoms of giardiasis are relatively similar to those of cryptosporidiosis, with a similar duration (1 to 2 weeks). However, the disease can cause some less common symptoms, such as itchy skin, hives, and swelling of the eye and joints. In children, severe giardiasis can be extremely detrimental, as it might delay physical and mental growth, slow development, and cause malnutrition.

NSF/ANSI 55-2022 Water Treatment System Classification

Class A systems (40 mJ/cm2), one of the two classifications of UV water treatment systems from NSF/ANSI 55-2022, are designed to disinfect and/or remove both Cryptosporidium and Giardia, along with bacteria and viruses, from contaminated water to a safe level.

Alternatively, Class B systems (16 mJ/cm2) are designed for supplemental bactericidal treatment of public or other drinking water that has been deemed acceptable by a local health agency.

The NSF/ANSI 55-2022 standard details the purification recommendations for these two UV water treatment system classifications, along with material performance guidelines. It also covers product literature and labeling information to be supplied by the manufacturer.

Changes to NSF/ANSI 55-2022

The 2022 edition of this American National Standard is the most recent, revising the 2021 edition of the same document. In addition to corrections and updates to references, the 2022 revision saw the following changes:

  • New language was added to allow installation, operation, and maintenance instruction manuals, as well as performance data sheets, to be provided online.
  • The minimum 2-L sample requirement was updated to a recommendation.
  • Storage instructions for coliphages, including establishing separate storage directions for working stocks vs. propagation freezer stocks, were updated.

NSF/ANSI 55-2022: Ultraviolet microbiological water treatment systems is available on the ANSI Webstore.

Changes to NSF/ANSI 55-2021

The 2021 edition of this American National Standard revised the 2020 edition of the same document. For any users of this standard that need to know the changes made to this revision, we’ve listed them below:

  • Updates were made to testing systems with LED bulbs.
  • Text in Figure 2 was updated to clarify collimated beam apparatus specifications.
  • Normative Annex 1, “Ultraviolet water treatment systems microbial reduction – MS-2 and T1 procedures,” and Normative Annex 2, “Ultraviolet water treatment systems microbial reduction – Qβ procedures,” were updated to reflect process improvement efforts of laboratory operations.
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