Desalination plants aren't a good solution for California drought
Enthusiasm for desalination tends to overlook its high costs, which stem in part from its enormous energy demand and weighty environmental footprint. The modern process, known as reverse osmosis, involves forcing seawater at high pressure through a membrane that screens out the salt, leaving behind a heavily brackish residue.
In Southern California, which has become more dependent on fossil-fueled electric generation since the shutdown of the San Onofre nuclear power plant, Carlsbad arguably will be moderating the effects of climate change on the region while also contributing to the greenhouse gas emissions that help cause it. (MacLaggan says Poseidon will buy carbon credits and restore local wetlands to offset the plant's environmental impact.)
"There are definite advantages to seawater desalination," says Heather Cooley, water program director at the Oakland-based environmental think tank Pacific Institute. "It's a reliable supply, independent of weather conditions like drought. But it's still among the most expensive water supply options."
Let's take a look at the hard realities. As big industrial facilities, desalination plants can't be plunked down just anywhere on the coast without destroying the qualities that attract people to the shoreline. Yet the plants need to be close to customers, with room for pumps, pipelines, inflows and outfalls.
Poseidon rejected three locations before settling on the Carlsbad site, which is next to NRG Energy's Encina Power Station. That allowed the new plant to share the seawater-cooled power station's water lines, which reduced its cost and its impact on marine life. Even so, according to a 2012 state appeals court ruling, the plant had to install extra equipment to reduce its marine impact in periods when Encina isn't running; if the power plant shuts down permanently, the desalination plant may have to submit a new environmental impact report.
The San Diego County Water Authority has committed to purchasing the plant's entire output for 30 years — a deal that was crucial for Poseidon's financing —
for about $2,100 to $2,300 per acre-foot, plus inflation. An acre-foot is 325,851 gallons, or about a year's usage for one or two five-member families. The county agency, therefore, will be paying at least $110 million a year, whether it needs the plant's water or not. San Diego water bills are projected to rise by an average of $5 to $7 a month to cover the cost.
The county judged that it might pay about that much in the future for other imported water, which makes the commitment look like a long-term hedge against a continuing water crisis. But desalinated water is far more expensive than other existing sources. San Diego currently pays $923 per acre-foot for treated water from the Metropolitan Water District.
The Pacific Institute reported in 2012 that San Diego could obtain recycled water for as little as $1,200 per acre-foot, and that the marginal cost of water obtained through conservation and efficiency measures was as little as $150.
The desalinization plants will be built, but not in the quantities to make up agricultural water during a major drought. Economics.
