This standard sets the minimum requirements for closed-vessel ultraviolet (UV) disinfection systems and equipment elements used for drinking water disinfection of Cryptosporidium, Giardia, and viruses. It does not include wastewater, reuse, or advanced oxidation treatment. Equipment and elements covered under this standard include UV reactors, related appurtenances, and reactor validation. This standard can be referenced for design, procurement, installation, and commissioning of UV disinfection equipment used in drinking water treatment.