Seattle Public Utilities Mami Hara, General Manager/CEO

Ultraviolet Light Disinfection Facility

  • UV reactors kill bacteria, viruses and other pathogens in water.

The Cedar Water Treatment Facility is among the first and is one of the largest facilities in the United States to use UV technology to disinfect drinking water. The UV light disinfection facility exposes water to high intensity light to inactivate the pathogens. UV light is the primary disinfectant barrier for Cryptosporidium and an additional disinfectant barrier against bacteria, viruses, and Giardia. UV light has many benefits: it is effective against chlorine-resistant pathogens such as Cryptosporidium, limits the amount of chemicals needed for disinfection, and it is not known to produce any byproducts. Following UV disinfection, chlorine is added to the water to provide an additional and residual disinfection barrier during water distribution. Lime also is added to make the water less corrosive.