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Recycled water research

Ensuring quality of King County Recycled Water through research and testing.

King County follows national research on recycled water and teams with the University of Washington to understand how recycled water works in the northwest. The results have been reassuring. Studies confirm our Class A recycled water uses are safe for people and the environment.

Healthy, safe plants

Recycled water contains nitrogen, phosphorus, and potassium – the same nutrients in fertilizer. Researchers found that plants grow as good or better when they are watered with recycled water compared to drinking water. And using recycled or drinking water makes no differences in amount of germs or metals in the plants or soil. Food crops grown with recycled water meet all federal safety standards and are safe for people to eat.


Good soil

Researchers found that using recycled water for irrigation helps the soil structure or “tilth.” Recycled water does not cause salts to build up in King County soils because we have good quality natural water and lots of rain

Some things don’t break down

Wastewater treatment plants are designed to treat biological waste. Some things do not break down during treatment. So King County works with people and industries to keep chemicals out of the system in the first place.

Scientists can find very tiny amounts of shampoos, soaps and medicines 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.

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

For the full report, click here.

In 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.

Recycled water has been studied for years. Learn more about different uses of recycled water and research at WateReuse Association: