Just when it appeared that California was finally warming up to desalination, we got a gusher of bad news last week that could threaten to set back future plants.

You may have seen where San Diego water authorities had such an overabundance of water they had to dump a half-billion gallons of treated water into a lake. Some of that included expensive desalinated water from a billion-dollar plant that opened in December. The overabundance occurred reportedly because conservation efforts have gradually reduced the demand for water there (and I presume winter rains cut water use even more just recently), yet San Diego is required by contract to buy desalinated water from its new Poseidon Resources plant. At the same time, the big water supplier, Metropolitan Water District of Southern California, said it couldn’t just shut off or even slow down the normal flow of water into that city. The result: Lots of water got poured into a lake near Chula Vista.

And that set off complaints that the city’s ratepayers are being “forced” to buy expensive water they don’t need. Already there are opinions online saying future desalination plants should not be built, and it’s not hard to imagine that pressure will build to stop the 15 desal plants proposed or under construction up and down the California coast.

That would be unfortunate because desalination plants, while not a silver bullet to slay California’s werewolf of a water problem, should be one part of the solution. They can supply, say, 5 percent to 20 percent of a city’s water needs. But, alas, thanks to what’s happening in San Diego, desal plants may become about as popular as nuclear power plants. Even though the real problems in San Diego appear to be a bad contract with Poseidon and a crazy lack of reasonable flexibility in the water district’s system.

Coincidentally last week, the Milken Institute Review in Santa Monica published an interesting essay on desalination. By Lawrence Fisher, the article pointed out that most of the knocks on desal plants have been minimized in recent years.

Take, energy use for example. Desalinated water used to take an ungodly amount of power, but now the improved process needs about one-fourth the energy it needed in the 1970s. Fisher wrote that the Poseidon plant’s water will use about 30 percent more power than fresh water to treat. Although he didn’t mention this, desal plants in Southern California would make great solar farms.

Lower energy use helps lessen the other traditional problem: cost. Desalinated water used to be prohibitively expensive. Now it’s only about double the usual cost; some plants in Israel and other places have narrowed the gap further. For San Diego, that means the new desalinated water will add $5 to $7 a month to a typical bill, which may well be an acceptable expense given the city now has a drought-proof source of water, Fisher wrote.

Environmental degradation is another concern with desal plants. But the industry has learned to place the pipes that take in water from the ocean well under the sea floor, minimizing ecological harm caused by sucking in fish eggs and the like. And the brine that results from the desalination process can be mixed with storm-water runoff and sprayed on the surface of the ocean. That results in reduced environmental damage.

Desalination does have problems and drawbacks, of course, but so does transporting water from Northern California or getting water from any other source.

The desal plants that could be built along the coast would go a long way toward permanently helping, but not solving, the state’s water shortage. It would be a terrible setback if San Diego’s bad experience washes away those desal plans.

Charles Crumpley is editor of the Business Journal. He can be reached at [email protected].