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Water Quality Testing
What Seattle Public Utilities Is Doing About Cryptosporidium
What is Cryptosporidium?
Cryptosporidium is a parasite commonly found in lakes and rivers that can cause gastro-intestinal disease.
There have been no known waterborne disease outbreaks in the Seattle area, and Seattle Public Utilities’ water is treated to remove Cryptosporidium.
If you have a weakened immune system (immuno-compromised), local and national health agencies recommend that you follow certain guidelines. These guidelines are described in the companion Cryptosporidium page (linked below).
How can Cryptosporidium be removed from water?
Public water providers, especially those that use surface water, use multiple barriers to reduce the number of oocysts and kill Cryptosporidium in water.
Since Cryptosporidium is resistant to traditional disinfection using chlorine, the best protective practices start with the protection of watersheds from contamination and include the use of optimized filtration and ozonation.
Currently, Seattle Public Utilities' watersheds are protected through the restriction of access by the general public. The watersheds are located in the Cascade Mountains, and are inhabited by deer, elk, and other warm-blooded animals which can be carriers of Cryptosporidium. Seattle Public Utilities is proceeding toward a multiple barrier approach to ensure that drinking water remains safe for the general population.
Filtration and ozonation facilities started operating on the Tolt River supply in February 2001. On the Cedar River supply, an ultraviolet and ozone disinfection facility is scheduled to be operational in 2004.
To date, Seattle Public Utilities has not had a known waterborne outbreak of cryptosporidiosis.
Related links
Cryptosporidium
Glossary of Drinking Water Terms
Tolt River Treatment Facility
Cedar River Treatment Facility
Water Quality Planning and Engineering
Water Quality Annual Reports
Water Quality Analyses
Links to other sites
Centers for Disease Control Information on Cryptosporidium
Environmental Protection Agency (EPA) Guidance for People with Severely Weakened Immune Systems (pdf)
EPA's Microbiology Home Page
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