OVERVIEW

Ultraviolet (UV) light has been used for many decades for disinfection of drinking water supplies worldwide. In North America, the use of UV light was more widespread for wastewater disinfection in the last quarter-century, and only more recently has UV light been considered for drinking water disinfection for a wide range of potable water systems. For disinfection of drinking water supplies in North America, UV disinfection was long assumed to provide effective inactivation of bacteria and viruses, but UV light was believed to be ineffective for inactivating protozoa at UV doses that would be cost-effective for implementation.

In 1998 and 1999, new research was published demonstrating that UV disinfection was capable of cost-effectively inactivating Cryptosporidium oocysts (Clancy et al., 1998; Dyksen et al., 1998; Bukhari et al., 1999). Where previous studies had focused on in vitro assays to indicate oocycst viability, these new studies utilized animal infectivity assays to directly determine the ability of the pathogen to replicate and cause disease. In the following years, several more studies confirmed these findings and demonstrated the effectiveness of UV disinfection for the inactivation of Giardia cysts as well (Craik et al., 2000; Danielson et al., 2001; Hayes et al., 2001; Oppenheimer et al., 2002; Campbell and Wallis, 2002; Linden et al., 2002a; Mofidi et al., 2002). Concurrently, new research showed that higher UV doses...