From Toilet to Tap

From Toilet to Tap

Facility uses sophisticated technology to transform wastewater into clean water.


3 - 12+


Engineering, Geography, Human Geography, Physical Geography, Physics, Social Studies, Economics

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Holding a plastic cup within the Orange County Water District’s

Groundwater Replenishment System (GWRS), program manager Shivaji Deshmukh announces a fact that might make some people’s stomachs turn.

“An hour and a half ago, this was treated sewage,” he says. “A day ago, it was raw sewage.”

Having complete faith in the project and its end result, Deshmukh then downs the water without blinking.

An ingenious method to fight California’s water shortage, the GWRS takes an unlikely resource—sewage flushed down the toilets in Southern California’s Orange County—and transforms it into drinking water that exceeds all state and federal drinking water standards.

Before taking the gulp of refreshing purified water, Deshmukh led me on a tour of the facility, which took about an hour, the approximate amount of time it takes the treated sewer water to pass through three processes before becoming drinkable. Costing $480 million to construct, the state-of-the-art water purification project has been up and running since January 2008.

The Groundwater Replenishment System is in an ideal location: just feet away from the Orange County Sanitation District (OCSD), where the sewage from northwest Orange County is treated. Every day, OCSD sends water over to the GWRS through a .8 kilometer (.5 mile) long, 2.4 meter (96-inch) pipe. Former public affairs manager for Orange County Sanitation District, Michael Gold, explains the kind of water his neighboring facility receives: “When it comes in [to the OCSD], it’s dirty,” he says. “It’s smelly. It’s full of viruses and junk. As it comes out of our plant, it looks clean, but it’s not clean enough to swim and bathe in.”

Currently, OCSD sends about 378 million liters (100 million gallons) of treated sewer water over to the GWRS for recycling every day. Gold says that amount of water is roughly enough to fill up nearby Anaheim Stadium, home to Major League Baseball’s Los Angeles Angels of Anaheim.

Three Processes

After OCSD sends treated water to the GWRS, it undergoes three processes to make it drinkable: microfiltrationreverse osmosis, and ultraviolet disinfection.

The first process is microfiltration. Deshmukh said this gets rid of bacteriaprotozoa, and suspended solids in the liquid by pushing it through a series of fiber membranes filled with tiny, hollow tubes. He compared it to drinking iced soda through a straw. The pollutants are like the ice, which are too large to be drawn up through the straw.

The water is propelled through the microfiltration membranes with giant, 600-horsepower engines. Following microfiltration, the water sits in a large holding tank.

“This R.O. plant is one of the biggest in the world,” Deshmukh said.

Inside, the facility looks like a warehouse filled with stacks of plastic pipes.

“The water we get here has been microfiltered, but now we have to take the organics, the pharmaceuticals, the viruses, and salts out of the water,” Deshmukh said.

During reverse osmosis, specially made plastic sheets allow the passage of water while harmful material as small as a molecule is separated out. “This is the heart of the treatment process,” Deshmukh explained. “This allows us to make the water potable.”

In reverse osmosis, conducted by OCSD, the water is pushed through plastic sheets by 1,000-horsepower engines. The program manager insists that the energy used in treating the water is worthwhile when compared to other methods of supplying Orange County with water. One popular method is shipping water from northern California.

Reverse osmosis uses a lot of energy, but when you compare it to pumping water over a mountain range [the Sierra Nevada, California], it’s less,” he said.

After Deshmukh taught me about the reverse osmosis process, we stepped outside into the Orange County sun and walked towards the final stage the former sewer water had to be put through. We stopped at a series of steel cylinders that are filled with ultraviolet light bulbs. Ultraviolet disinfection destroys any of the water’s remaining viruses.

“This is the last step,” Deshmukh said. “After this, we actually add minerals back to the water.”


It’s here where Deshmukh and I tip back our plastic cups filled with the newly treated water and drink in a liquid that may have been swirling around a toilet bowl just a day ago. But this water actually has months to go before it will flow out of any of Orange County’s taps.

About 132 million liters (35 million gallons) of the water treated by GWRS is injected into Orange County’s seawater barrier. The barrier, a series of wells that function like a dam, helps keep the region’s aquifers, or underground freshwater supply, from being overtaken by seawater from the nearby Pacific Ocean.

About 246 million liters (65 million gallons) of the water is pumped 21 kilometers (13 miles) away to Anaheim, where it is discharged into several lakes. From there, it joins the region’s rainwater and settles into aquifers as groundwater. In approximately six months, the groundwater is chlorinated by the cities of Orange County and sent to taps for personal and business use.

As of 2015, the Orange County Water District treated 378 million liters (100 million gallons) of water daily, the amount that would meet annual water needs of 850,000 people.

In addition to creating a renewable source of fresh water for the area’s growing population, another benefit is that the GWRS reduces the amount of treated wastewater discharged in the Pacific Ocean.

Though the initial idea of drinking reclaimed water might make some stomachs turn, the success of Orange County’s Groundwater Replenishment System has caused a turn in California’s thinking about the idea of transforming sewer water into drinking water. This change has resulted in a series of proposals for similar facilities across the state.

Fast Fact

Water Wisdom
Before the Groundwater Replenishment System began processing treated sewer water in January 2008, the Orange County Water District's Water Factory 21 was the first facility to use reverse osmosis to make municipal sewer water into purified drinking water.

Media Credits

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Stuart Thornton
Jeannie Evers, Emdash Editing, Emdash Editing
Kara West
National Geographic Society
Last Updated

April 29, 2024

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