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About SPU
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Water System
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Water Quality & Treatment
Giardia
What Giardia is
Giardia lamblia is a microscopic protozoan which, when ingested, can cause giardiasis. Giardiasis is a gastro-intestinal disease manifested by diarrhea, fatigue, and cramps. Symptoms can last anywhere from a few days to months.
Warm blooded animals, such as elk, deer, muskrats, beavers, domestic or farm animals, and humans can be hosts for this protozoan. Giardia is excreted into the environment from the fecal material of the warm-blooded hosts. It is then washed into lakes, rivers, and streams. For this reason, consumption of untreated water while hiking, camping or at any time is not recommended.
Giardia can also be spread in day care or health care settings from inadvertent fecal/oral contact (diaper changing, food preparation, etc.). Also, travelers to foreign countries often contract giardiasis.
Monitoring and water treatment for Giardia
Seattle Public Utilities has monitored for Giardia since 1988. Our monitoring has sometimes found small concentrations of Giardia cysts in the water prior to treatment.
Disinfection with chlorine is very effective in destroying Giardia in water. This is Seattle's current treatment method on the Cedar River supply. Additional treatment processes have been added on the Tolt River supply; and additional ones will be added on the Cedar River supply in the near future to provide additional water quality protection.
Relevant water treatment regulations and compliance
The United States Environmental Protection Agency’s Surface Water Treatment Rule water treatment regulation was developed to ensure that public water systems using unfiltered surface waters provide adequate disinfection to reduce Giardia concentrations in water by at least 99.9%.
Seattle Public Utilities provides continuous disinfection and monitoring of its water supplies to demonstrate that effective treatment is being carried out. SPU's water treatment achieves the mandated 99.9% Giardia reduction on a daily basis. Historically, we have provided significantly greater reductions than the minimum 99.9% most of the time.
Meeting and exceeding water standards
Seattle's treated drinking water -- the water that customers receive -- has always met or been better than drinking water standards. Seattle - King County Public Health Department (SKCPHD) and the Washington State Department of Health (WDOH) continue to indicate that there are no known waterborne disease outbreaks attributable to the drinking water system.
Related links
Glossary of Drinking Water Terms
Tolt Treatment Facility
Cedar Treatment Facility
Links to other sites
United States Environmental Protection Agency: Interim Enhanced Surface Water Treatment Rule
United States Environmental Protection Agency: Long Term 1 Enhanced Surface Water Treatment Rule
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