Interest in using ultraviolet (UV) light to disinfect drinking water is growing among public water systems (PWSs) due to its ability to inactivate pathogenic microorganisms without forming regulated disinfection byproducts (DBPs). UV light has proven effective against some pathogens, such as Cryptosporidium, that are resistant to commonly used disinfectants like chlorine.

The United States Environmental Protection Agency (EPA) developed the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) to further reduce microbial contamination of drinking water. The rule requires additional treatment for some PWSs based on their source water Cryptosporidium concentrations and current treatment practices. UV disinfection is one option PWSs have to comply with the additional treatment requirements.

The design, operation, and maintenance needs for UV disinfection differ from those of traditional chemical disinfectants used in drinking water applications. EPA has developed this guidance manual to familiarize states and PWSs with these distinctions, as well as associated regulatory requirements in the LT2ESWTR. Particularly important design and operation considerations include monitoring, reliability, redundancy, lamp cleaning and replacement, and lamp breakage. Regulatory requirements include UV dose, UV reactor validation, monitoring,
reporting, and off-specification compliance.

EPA developed the requirements for UV disinfection in the LT2ESWTR and the guidance in this manual solely for PWSs using UV light to meet drinking water disinfection standards established under the Safe Drinking Water Act (SDWA). EPA has not addressed and did not consider the extension of these requirements and guidance to other applications, including point-of-entry or point-of-use devices for residential water treatment that are not operated by PWSs to meet SDWA disinfection standards.

Bibliographic information

EPA (2006). Ultraviolet Disinfection Guidance Manual for the Final Long Term 2 Enhanced Surface Water Treatment Rule EPA

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