Those savings reduce the amount of water available for recycling, local officials noted.

Californians could further reduce urban water use by 30% to 48% by steps such as replacing inefficient appliances and installing low-water use landscaping, according to a Pacific Institute report last month.

The major constraint for more local water recycling is Santa Rosa’s collaboration with Houston-based Calpine Corp., the nation’s largest geothermal power producer, which operates 13 power plants at The Geysers, straddling the Sonoma-Lake county line in the Mayacamas Mountains.

Steam wells, some deeper than 2 miles, tap superheated steam from water in contact with hot, porous and permeable rock. At the surface, steam runs through pipes to the power plants, spinning turbines that generate 725 megawatts of green energy around the clock.

Under a contract with Calpine that runs until 2037, Santa Rosa is required to provide 90% of the targeted 4.6 billion gallons of recycled water a year or pay penalties.

Reduced deliveries are allowed for natural catastrophes, such as wildfire and earthquake damage, but current drought conditions would not trigger that provision because there is enough water to fulfill the contract, said Jennifer Burke, director of Santa Rosa Water.

“The Geysers provides a critically important piece of our wastewater treatment system,” she said. “We need it to dispose of our wastewater.”

Even if the city could curtail water delivery to The Geysers, it is prohibited from spraying more recycled water on farmland than the crops require, Burke said.

Calpine has so far shown no interest in renegotiating the contract, she said.

Officials ponder recycling costs, options

Santa Rosa’s last look at the prospects for expanding water recycling said it did not pencil out — “not cost effective for the foreseeable future,” according to the city’s 2020 Urban Water Management Plan.

Burke said it would cost tens to hundreds of millions of dollars to install the necessary pipes, painted purple to distinguish them from ordinary potable water pipes.

Even at its current historically low level for this time of year, 2,700-acre Lake Sonoma west of Cloverdale, the North Bay’s largest reservoir, holds a two- to three-year supply of water, she said. It has helped the region support growth while withstanding several droughts over the past four decades.

But city and county officials and water authorities are not downplaying the prospect of running low on drinking water around the North Bay, which has no connections to the state and federal water systems. Rainwater runoff into the Russian River watershed, along with groundwater, constitute the main supplies.

“We’re always looking at our options,” Burke said, noting that conservation, surface water, groundwater and recycled water are in play. “We’re planning for the future with additional dry years,” she said.

There are opportunities for expanded water recycling in the county’s northern reaches, including Healdsburg, Cloverdale, Dry Creek Valley and Alexander Valley, said Grant Davis, general manager of Sonoma Water, the dominant water wholesaler and a key player in recycling efforts over the past two decades.

“As (potable) water becomes more constrained, you have to look further, you have to be more innovative,” he said. “You need to work hard to make these projects pencil out,” including the prospect of tapping ratepayers for support.

Adding a fourth step to the wastewater treatment process to transform sewage into potable water is an option, Davis and Burke said, noting that it is already happening in the state.

“Everything is on the table.” Burke said.

Southern California program leads way

Orange County’s $481 million Groundwater Replenishment System, in operation since 2008, produces 100 million gallons of recycled water per day through an advanced purification process that includes microfiltration, reverse osmosis and ultraviolet light with hydrogen peroxide.

Two-thirds of the treated water is piped to recharge basins in Anaheim, replenishing groundwater that provides 75% of the water for more than 2.5 million Orange County residents — a system known as indirect potable water reuse.

Billed as the world’s largest potable water purification facility, Orange County’s system uses one-third of the energy required to desalinate seawater and half the energy needed to import water from Northern California.

No agency is currently allowed to produce recycled water for direct potable use, but the Water Resources Control Board is required by law to develop regulations for direct potable use — putting it into public water supplies — by the end of 2023.

The regulations will provide options to California communities “working to diversify their water supply portfolios in the face of recurring drought and climate change,” Rebecca Greenwood, a water board engineering geologist, said in an email.

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