NSF/ANSI 55-2022 Water Treatment System Classification

Source : ANSI

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.

7. Elective performance claims – Test methods
7.3 Microbiological performance
7.3.1 Microbial performance testing
Component filters or other media that may interfere with the testing of a system shall be removed or bypassed during the test.
Microbiological methods for stock culture preparation, enumerations / analysis, storage, and stock challenge concentration for challenge test for Qβ coliphage shall be performed as specified in Annex N-2.

7.3.1.1 Class A systems
A Class A system shall deliver a UV dose to achieve a 3.50 log reduction of the challenge organism concentration in the influent at the alarm set point when the system is tested in accordance with Section 7.3.1.7 or 7.3.1.8 as applicable.

7.3.1.2 Class B systems
A Class B system which is evaluated with the UV source irradiance at normal output shall deliver a UV dose to achieve a 2.00 log reduction of the challenge organism concentration in the influent when the system is tested in accordance with Section 7.3.1.7 or 7.3.1.8 as applicable.
A Class B system which is evaluated with the UV source irradiance at 70% of normal output, or at the alarm set point, shall deliver a UV dose to achieve a 1.50 log reduction of the challenge organism concentration in the influent when the system is tested in accordance with Section 7.3.1.7 or 7.3.1.8 as applicable.