Ultraviolet Microbiological Water Treatment Systems

NSF ANSI 55 2018 Ultraviolet microbiological water

Of the many objectives undertaken at federal, state, and local levels, guaranteeing access to safe, clean water is one of the utmost necessities. However, many users 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, as addressed in 1987’s Report of Task Force on Guide Standard and Protocol for Testing Microbiological Water Purifiers, can be achieved through the use of ultraviolet radiation (UV).

The first edition of NSF/ANSI 55 was released by NSF International with considerations discussed in the expert task force’s report, and subsequent revisions have built off that knowledge. NSF/ANSI 55-2018 – Ultraviolet microbiological water treatment systems, the newest revision, covers the minimum guidelines 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 through NSF/ANSI 55-2018 – Ultraviolet microbiological water treatment systems guidance, users can reduce considerably 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 55-2018 – Ultraviolet microbiological water treatment systems guidance include:


Cryptosporidium is a microscopic parasite which 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 customarily spread through drinking water and recreational water that has been contaminated with feces from infected individuals as well.

Giardia Cryptosporidium Water UV

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.

Ultraviolet Microbiological Water Treatment System Classification

Class A systems (40 mJ/cm2), one of the two classifications of UV water treatment systems from NSF/ANSI 55-2018 – Ultraviolet microbiological water treatment systems, 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 55-2018 – Ultraviolet microbiological water treatment systems standard details the purification recommendations for these two UV water treatment system classifications, along with material performance guidelines and product literature and labeling information to be supplied by the manufacturer.

NSF/ANSI 55-2018 – Ultraviolet microbiological water treatment systems is available on the ANSI Webstore.

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