Recycled Water

Background

Recycled water is highly treated wastewater that has been filtered and disinfected to remove solids and other impurities. Simply put, recycled water is water that is used more than once! 

Recycled water is used across the country (i.e. California, Florida, Arizona) and internationally as a sustainable water source to irrigate food crops, but is underutilized and underdeveloped here in Washington state. More irrigation use of recycled water would reduce river water withdrawals, protecting salmon and other wildlife that depend on cool and clean water. 

The Driver to Use Recycled Water

Many of our states rivers and streams are overdrawn by out of stream uses during the late summer when flows are absolutely vital for the species survival of Salmon, steelhead and other aquatic species. Demand for freshwater resources in Washington is outgrowing availability. This availability is exacerbated by climate change, increased demand from population growth, and limits to new water rights. 

These conditions compel a new way of thinking about agricultural production and irrigation sources, for the health of rivers, and climate resilient and sustainable agriculture.

A Sustainable Water Source

Irrigating with recycled water in specific basins can serve as a vital tool to protect flows for salmon, relieving rivers of agricultural surface diversions. 

Recycled water irrigation is already standard practice in some regions of the United States, including California’s Salinas Valley where it has been used to irrigate fruits and vegetables since 1998, providing more than 90% of the irrigation supply. In Washington state, recycled water has yet to be fully realized as a water source for food crops. 

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Active Projects

Sammamish Valley Recycled Water Project

Tapping into a Sustainable Water Source of Water for Agriculture

The Sammamish Valley Recycled Water Project aimed to evaluate perceptions and address concerns about the safe use of recycled water on food crops and to reduce the reliance on the Sammamish River for irrigation. More irrigation use of recycled water would reduce river water withdrawals, protecting salmon and other wildlife that depend on cool and clean water.

Although recycled water is strictly regulated, there is growing concern about trace amounts of unregulated chemicals in recycled water that might be exposed to people and the environment. These chemicals, known as contaminants of emerging concern or CECs, come from various products we use every day, like medicines, shampoos, food packaging, drinks, and clothing.

Click on the tabs below to learn more about each project component!

Project Components

In spring of 2020, a demonstration garden was built on the grounds of King County’s Hollywood Pump Station in Sammamish Valley, WA. The Sammamish Valley is one of five designated agricultural production districts in King County and is home to many vegetable farms.

In order to address concerns about the use of recycled water on food crops, an experiment was designed to provide a local example of how the recycled water compared as an irrigation source to river water. Because recycled water is an alternative irrigation source to river water, we designed the research garden so that the only variable in the research was the water source. Sixteen raised garden beds were installed and planted with kale and carrotshalf of which were irrigated with recycled and half were irrigated with Sammamish River water.  

The water, soil, and plants were tested for hundreds of contaminants of emerging concern, also referred to as CECs, from each water source. The study looked extensively at what CECs were present in the crops irrigated with both water sources. What did we find? Some CECs are present, but at such low concentrations you would need to eat thousands of pounds of the produce to reach a single dose of certain drugs.

Overall, crops irrigated with recycled water were found to not be a significant source of CECs to humans or the environment. Recycled water was also found to provide benefits to crops in the form of added nutrients. Kale grown with recycled water grew more than double the size of kale irrigated with river water due to the extra nutrients in recycled water!  

Although recycled water is already used to irrigate food crops in other parts of the USA, providing a local example under local  cultivation conditions, is important to make recycled water a viable water alternative for Sammamish Valley producers. 

To learn more about how King County uses recycled water, visit their website.

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Sammamish Valley Recycled Water Project Partners and Funders are working together to re-water Washington rivers and streams. 

Project Partners

Washington Water Trust

King County Recycled Water

Washington State University Puyallup Extension

Project Funders

King Conservation District

Bullitt Foundation

King County WaterWorks