Seventeen plants are in planning stages along the coast to convert salt water from the ocean or bays, including one near Concord that would serve every major water agency in the Bay Area.
That plant is tentatively targeted to open in 2020, but could be kick-started earlier in an emergency, officials say - and once online, would gush at least 20 million gallons a day of drinkable water.
Starting up this string of desalination plants would be no easy skate, though. Machines that filter salt out of water still face the same opposition they have for generations from critics who say they are too expensive to run, kill fish as they suck in briny water, and spew greenhouse gases into the air from the energy they require to run.
But in recent years, as technology and techniques for desalination have improved, such plants have gained momentum - enough so that in Carlsbad near San Diego, the biggest desalination facility in the Western Hemisphere is under construction and set to begin operation in two years.
During the last major California drought, from 1985 to 1991, there was enough interest in desalination that a large plant was built to serve Santa Barbara. But it was promptly mothballed after being finished in 1992. By then, with the drought over, water from traditional sources was again about two-thirds cheaper than the $3,000 per acre-foot it cost to produce the plant's water.
An acre-foot is equivalent to one acre covered by water 1 foot deep, enough to supply two families of four for a year.
That cost gap has narrowed, however. With better screens and technology that helps the plants power themselves by recycling the energy used to suck in water - in a way, like a hybrid car regenerates power from its own motion - the typical cost of running desalination plants can dip below $2,000 an acre-foot. Because pulling up groundwater from wells and recycling water can now cost the same or more, desalination is suddenly relatively affordable for many areas - such as the Bay Area.
Surface water from reservoirs and mountain runoff, in plentiful years, can be as cheap as $100 an acre-foot. But that bargain has become scarce in the drought.