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Monterey One Water leads Northern California in turning wastewater into drinking water

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Monterey One Water
The Monterey One Water wastewater reuse complex north of Marina. Pure Water Monterey operates under the big red roof.

Among the humming machines and maze-like pipes of the water purification plant just north of Marina, Mike McCullough fills a cup with water from a row of faucets.

"I'll drink it first," he said, before tipping the cup back.

The water is remarkable because it looks — and tastes — completely ordinary. But the water’s journey to McCullough’s plastic cup involved a series of tanks, screens, and filters that transformed it from raw sewage to drinking water.

"Nobody can really tell the difference," said McCullough, who is the director of external affairs for Monterey One Water, the utility that manages all parts of the wastewater treatment process.

A third of the drinking water that flows through Monterey Peninsula taps is derived from wastewater treated at the Pure Water Monterey plant. And after a planned expansion in 2024, recycled wastewater will make up more than half of the Peninsula’s drinking water supply.

If approved, the expansion would cement the publicly-owned Monterey One Water as an industry pioneer.

The Pure Water Monterey plant is just one project under Monterey One Water’s umbrella, which has delivered potable purified wastewater to California American Water’s peninsula customers since 2020. Monterey One Water oversees the collection of wastewater, its multi-stage treatment, and the delivery of treated water to Peninsula customers and Castroville farms.

The purification process involves a state-of-the-art method using microscopic membrane filtration and reverse osmosis to destroy all the harmful pathogens and pollutants.

“We can recover about 81 percent of the water that goes through that treatment process,” McCullough said. “So, 10 gallons go in. We get eight gallons (of purified drinking water) that come out.”

Monterey One Water
Inside the Pure Water Monterey plant where wastewater is purified for drinking. It was built with room to expand.

The water reuse process starts outdoors in a vast compound where sewage — and everything else that goes down the drain — swirls through massive tanks of wastewater. After sticks and rags are screened out, bacteria begin to break down the larger compounds.

There are six stages of treatment before the water reaches safe drinking levels. The early stages, in these outdoor tanks, produce water safe enough to be pumped into Monterey Bay and out to farms in nearby Castroville for irrigating crops.

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Suzanne Saunders / KAZU News
Wastewater is broken down by bacteria in massive outdoor treatment tanks.

Only a quarter of the wastewater is pumped indoors to undergo the more costly purification process at the Pure Water Monterey plant. There, the next four stages are monitored through a computerized network of shiny pumps, pipes, and gauges. McCullough said the resulting water is so pure that minerals like calcium have to be added back in to stabilize the water molecules, so they don’t leach metal from the pipes. Tests show the final product exceeds government drinking standards.

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Suzanne Saunders / KAZU News
The highly computerized advanced purification process is monitored 24/7 from a control room on the M1W grounds.

There are six similar purification plants in Southern California, but Pure Water Monterey is the first of its kind in Northern California. Paul Sciuto, the general manager of Monterey One Water, said the operation is unique because it takes in four sources of wastewater — not just sewage, but also runoff from storm drains, from agricultural irrigation ditches, and from an enormous amount of wastewater called agricultural wash.

That “ag wash” comes from water used to pre-wash all the packaged lettuce and veggies from the Salinas Valley. Ag wash alone, Sciuto said, generates four million gallons of drain water a day.

Supporters of this full-cycle reuse system say it could solve the Monterey Peninsula’s chronic water shortage.

Across the West, water starved communities are watching the water reuse model and reassessing the value of their own wastewater. In Santa Cruz County, Pure Water Soquel is building a water purification plant to replenish its groundwater supplies.

But water recycling is still fairly rare.

“In California, we only treat about 15 to 18 percent of our wastewater and reuse it,” said Peter Gleick, the founder of the Pacific Institute, a global water think tank based in Oakland.

The Pure Water Monterey expansion project will be entirely powered by methane from the nearby public landfill at the Monterey Regional Waste Management District — a model that Gleick said was developed by the East Bay Municipal Utility District along San Francisco Bay.

There, methane is captured from sewage instead of a landfill, then converted to electricity to power the plant that treats the sewage.

“They actually produce more energy than they use. So it’s a net positive,” Gleick said. “They burn methane, which turns it to CO2. That’s still a greenhouse gas, but it’s less severe than methane.”

Still, Gleick says we could do more.

“All along California’s coast, we collect wastewater, partially treat it, and dump it back in the ocean. Increasingly, highly treated wastewater is seen as a source of reliable supply that ultimately, we're going to have no choice but to turn to.”

Monterey One Water’s Paul Sciuto agrees.

“It's a shame to use water once and dispose of it into the ocean,” he said.

Currently, Monterey One Water is finalizing designs to expand Pure Water Monterey and increase production. All of the potable water will continue to be delivered to Cal Am, the private water company that supplies water to the Monterey Peninsula’s six cities and the unincorporated areas of Carmel Valley and Pebble Beach.

Ian Crooks, Cal Am’s vice president of engineering, says the company fully supports the recycle model and is partnering with Monterey One Water to build pipes and other infrastructure for the project’s expansion. But the company has said it doubts recycled water will be enough to solve the shortage.

Instead, Cal Am champions desalination — the more costly process of removing salt and other particles from seawater to make it suitable for drinking. The company has argued desal is the only long term drought-proof solution for the peninsula’s water woes.

Cal Am has pushed for a desalination plant along Monterey Bay for almost two decades. Their proposal will go back before the California Coastal Commision next year.

The Pacific Institute’s Gleick believes desalination should be a community’s last option, after “cheaper, faster and more environmentally smart” alternatives have been tried, like stormwater capture and wastewater reuse.

For now, the Pure Water Monterey expansion project is the only new source of water developed for the Peninsula’s 100,000 customers. Monterey One Water still needs approval from the California Public Utilities Commission to start construction. If all goes as planned, the bigger purification plant will be in full operation by 2024.

Meanwhile, water supplies are shrinking. Cal Am is under state orders to sharply reduce its draws from the Carmel River by Jan. 1, 2022, and water rationing could be ordered in 2023. Whether conservation and water recycling will solve the shortage remains to be seen.

Cal Am is one of KAZU's many business supporters.