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Although reclaimed water has been researched and used in other parts of the world for decades, the King County Wastewater Treatment Division wants to be sure we fully understand the quality, potential uses and safety of our own locally generated reclaimed water in our local environment.

With science rapidly changing, King County keeps current on national research and news just in case something relevant or interesting crops up, but for the most part it’s the local results that matter the most to our customers.

Because we play on local soccer fields and golf courses and because we eat produce and buy flowers at our farmers markets, King County contracted with researchers at the University of Washington since 2007 to perform local and independent research to determine the safest and best uses for our reclaimed water. Where else to obtain the best-available science about public health and environmental impacts about our own backyards than right here in our own backyard?

The results have been reassuring! Studies from the University of Washington have confirmed our Class A reclaimed water uses are safe for people and the environment.

Recycled Water Supports Healthy and Safe Plants

University of Washington research found no difference in presence of pathogens or metals in plant tissue or soil between plants irrigated with recycled water and tap water. Recycled water contains nitrogen, phosphorus, and potassium- the same nutrients in fertilizer. Researchers found all physiological measures were equal or better results than plants irrigated with tap water in the study. Food crops grown with recycled water met all federal safety standards for human consumption.



Recycled Water Maintains Soil Conditions

Research done by the University of Washington found use of recycled water for irrigation preserves soil tilth. Salinity, pH and nutrient levels in soil irrigated with recycled water were maintained. Many plants benefited from the additional nutrients supplied in recycled water.



Recycled Water is Safe

Recycled water is produced to remove the “bad” stuff like bacteria and other pathogens in water, but keep the “good” stuff in water like nutrients that plants can use. King County Recycled Water contains almost zero total coliform making it cleaner than many of our region’s lakes and streams sometimes used for irrigation.

No doubt about it, recycled water is as a clean or cleaner than many of the waterways we swim and splash around in. But very small amounts of shampoos, soaps and medicines can be found in recycled water. Local and national research shows a person would have to work fields irrigated with recycled water for 28,000 years before being exposed to the equivalent of one tablet of ibuprofen. Learn more about a study on personal care products at




Research Studies

University of Washington researchers conducted a two-year study to determine the food safety and nutrient value of food crops irrigated with reclaimed water.

For the full report, click here.

SunflowersIn 2008, scientists from the University of Washington began a two-part study to determine the safety of vegetables irrigated with reclaimed water. This study also examined the growth, physiology and aesthetics of ornamental and vegetable plants irrigated with reclaimed water.

For the full report, click here.

hand-grass-150In July 2008, researchers at the University of Washington conducted a six-month greenhouse comparison study to address concerns from potential customers regarding turf growth response, salinity, and the fate and transport of personal care products and pharmaceuticals.

For the full report, click here.


Washington State has strict regulations regarding the purity of water used to recharge groundwater sources. This study tested whether soil can act like a filter that influences the fate and transport of chemicals introduced by infiltrated water. University of Washington researchers conducted a two-year study to test the effects of two types of locally produced recycled water on two of the soil types found in King County.

Recycled water has been studied for years. Learn more about different uses of recycled water and research at “A Thirsty Planet”:

WateReuse Association:

For more information about the recycled water program, please contact us at: