What is Wastewater?

Water that has been used in your home, a business, or in industrial processes is known as “wastewater.” Once it has passed down the drain, wastewater is sent to a treatment facility for processing. At the wastewater treatment facility, various biological and chemical processes are used to remove some of the pollutants from the water. The partially treated wastewater is then discharged into the ocean, a river, or other waterway. Since the early days of water sanitation projects, wastewater has generally been seen as a liability to be dealt with and discarded, but modern technologies and adaptive thinking have begun to reframe wastewater as a valuable resource that, after advanced treatment, may be returned to a city’s water supply as local, sustainable freshwater. For more on wastewater, check out our “Where does our water go?” page.

Wastewater Recycling

Wastewater recycling is the process by which wastewater is filtered to remove solids and then further treated to a level necessary either for human consumption – called “potable reuse” – or for irrigation or commercial applications – locally dubbed “purple pipe.” This advanced, multi-stage process, similar to (but far less energy-intensive than) that used in seawater desalination, results in useful, high-quality freshwater, as well as a waste product known as “sludge” which is then processed for a variety of purposes, including fertilizer.

Rethinking the Status Quo

In the late 1990s, Coastkeeper and its partners began to see a better solution to the water supply and wastewater management status quo. As a semi-arid region reliant on expensive, environmentally taxing water imports from far-flung sources to meet its freshwater demands, San Diego’s practice of using that water only once before discharging it into the sea began to seem increasingly wasteful and unsustainable. By treating and reusing wastewater – a practice already employed by the “upstream” users of our water supply – San Diego could adopt a win-win approach to water supply management that maximized the use of imported water and minimized polluted discharges into the ocean.

San Diego’s Pure Water Project

After years of research, advocacy, and legal action, San Diego Coastkeeper, along with our environmental partners at CERF, Surfrider Foundation San Diego, and San Diego Audubon Society, signed a cooperative agreement with the City of San Diego obligating the City to implement the region’s first large-scale wastewater recycling project. By the full completion date in 2035, the Pure Water project will provide 83 million gallons of locally-sourced drinking water per day, meeting nearly one-third of San Diego’s drinking water needs. Additionally, this multi-benefit project will result in a substantial reduction in partially-treated wastewater discharges into the ocean, serving to protect the health and water quality of our coastal waters. In the meantime, Phase I of the project is scheduled to bring 15 million gallons per day of safe, clean, sustainable water to San Diego households by 2022. Inspired by the ongoing success of the project, other water agencies across the region and state are actively researching researching potable reuse projects of their own. To learn more about Coastkeeper’s involvement with the Pure Water project, check out our page on multi-benefit water management.