By David Bentley

In today’s society, people are becoming more and more aware of issues surrounding consistent, good quality potable water for human consumption. They’re getting their information from various media sources including magazines, newspapers, television and the Internet. Plus, they’re looking for different water treatment devices to meet their growing needs.

Manufacturers are also using this information to design the types of systems to meet the various needs and desires of their customers.

This combination of user awareness, manufacturing initiative and a growing number of private wells and users pulling potable water directly from local lakes, has allowed for the increase in certification activity to the newly revised ANSI/NSF Standard 55—Ultraviolet Microbiological Water Treatment Systems.

Change is good
Standard 55 was written to establish the minimum requirements a manufacturer will need to become certified for a Class A or B ultraviolet (UV) system. Depending on the class that a manufacturer would like to claim, systems certified to this standard may be used on either microbiologically safe or unsafe water.

Class A point-of-entry and point-of-use (POU/POE) devices are designed to disinfect and/or remove microorganisms, including bacteria and viruses, from contaminated water to a safe level. They aren’t intended for treatment of water that has an obvious contamination source such as raw sewage; nor are systems intended to convert wastewater to microbiologically safe drinking water. Class A systems are capable of delivering a UV dose, at a wavelength of 254 nanometers (nm), to at least 40 milliJoules per square centimeter (mJ/cm²) at the alarm set point—the point where a manufacturer will set its UV sensor to activate the system alarm.

Class B POU systems are designed for supplemental bactericidal treatment of treated and disinfected public drinking water or other drinking water tested and deemed acceptable for human consumption by the state or local health agency having jurisdiction. Class B systems aren’t intended for disinfection of microbiologically unsafe water but are designed to reduce normally occurring nonpathogenic or nuisance microorganisms only. The systems are capable of delivering a UV dose, at 254 nm, to at least 16 mJ/cm² at 70 percent of the normal UV lamp output or alarm set point.

Standard 55 was revised in January. The majority of these changes affect the Class A portion of the standard.

What do they mean?
The previous (2000) version of ANSI/NSF Standard 55 included, for Class A systems, that these systems be capable of producing a UV dosage of at least 38 mJ/cm². Standard 55’s latest version requires these systems be capable of producing a UV dosage of at least 40 mJ/cm² at the alarm set point. This change was initiated to bring this requirement in line with current international standards.

The 2000 version of Standard 55 required that Class A systems be challenged using Bacillus subtilis as a surrogate organism. This has been replaced with MS-2 coliphage in the updated version. The surrogate organism was changed to MS-2 coliphage because it’s better to handle and use in the laboratory. Additionally, MS-2 coliphage possesses an equivalent or higher resistance to UV than Bacillus subtilis. This increased resistance provides another level of safety and a higher level of confidence in the performance of the device. MS-2 coliphage also is non-pathogenic, inactivation is linear across many dose ranges, and analysis results can be obtained within eight hours. This change was initiated based on information provided to the NSF Joint Committee. This information referenced the German standard.

The 2000 version of Standard 55 included the requirement that if a cyst reduction claim were made, the system incorporated a cyst reduction filter installed upstream of the system. This system needed to meet the requirements of ANSI/NSF Standard 53 for health effects. The 2002 version of Standard 55 allows the scope of the Class A system to include a claim for the inactivation of Cryptosporidium and Giardia. This addition is granted based on the Class A requirements’ higher UV dose and studies that show inactivation of cysts at this dose level. The general cyst claim can still be made if the system incorporates a filter in compliance with Standard 53 installed upstream of the system. This use of a filter upstream will not result in a higher certification. The “general cyst claim” is from the “definitions” in Standard 53. This definition also includes the Toxoplasma oocyst and the Entamoeba cyst.

The latest version of ANSI/NSF Standard 55 includes an improved quality assurance/quality control (QA/QC) procedure not referenced in the standard’s previous version. Prior to testing and during generation of the dose response curve, the sampling requirement has been increased to three data points for each pre-determined dose. This improved procedure ensures propagation, harvest and preparation of the challenge stock will produce a homogenous and monodispersed suspension when introduced into the UV system.

What’s still needed?
The material extraction protocol hasn’t changed; however, a new health concern category has been created. This new health concern category is called the Maximum Contaminant Concentration (MCC). These MCCs have been set apart as they’re not Maximum Drinking Water Levels (MDWLs), but they are recognized contaminant levels established by a recognized regulatory agency, such as the U.S. Environmental Protection Agency (USEPA) or Health Canada.

The structural integrity testing requirements are still present; the 2002 version of Standard 55 clarifies these requirements for component certification. To qualify a system to Standard 55, a 15-minute hydrostatic pressure test is needed. Cyclic pressure testing has yet to be included as a requirement for the certification of a system.

A large number of North Americans draw their water from shallow wells and local surface waters. With the potential for bacteria, protozoa and viruses showing up in these source waters, a system certified to ANSI/NSF Standard 55 may be able to meet the needs to provide a higher level of confidence in the quality of potable water.

Today’s consumer is obtaining a greater amount of information about their water quality and their water quality needs. ANSI/NSF Standard 55 certification, specifically to Class A systems, can provide many of these users with another assurance of quality potable water.


  1. Clancy, J.L., Z. Bukhari, T.M. Hargy, J.R. Bolton, B. Dussert and M.M. Marshall, “Using UV to inactivate Cryptosporidium,” Journal of the American Water Works Association (JAWWA), 92 (9) 97-104, 2000.
  2. Hargy, T.M., J.L. Clancy, J.P. Durda, D.G. Korich and M.M. Marshall, “Susceptibility of Multiple Strains of Cryptosporidium parvum Oocysts to UV light,” proceedings IUVA Congress, Washington, D.C., 2001.
  3. Shin, G-A, K.G. Linden, G. Faubert and M.D. Sobsey, “Low pressure UV inactivation of Cryptosporidium parvum and Giardia lamblia based on infectivity assays and DNA repair of UV-irradiated Cryptosporidium parvum Oocysts,” proceedings, WQTC 2000, Salt Lake City, Utah, 2000.

About the author
David Bentley is a senior program representative in the Drinking Water Treatment Unit program at NSF International in Ann Arbor, Mich. He has been with the water program for nine years. Bentley can be contacted at (800) 673-6275, (734) 769-0109 (fax) or email: [email protected].


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