From saltwater to drinking water?

California considers desalination as a remedy for water woes

 

On the expansive beaches of California’s central and southern coasts, with the state mired in its worst drought in history, one is reminded of Samuel Taylor Coleridge’s ancient mariner. There is ocean aplenty – water, water, everywhere – but not a drop to drink.

Now, several coastal communities are looking at all that seawater as a possible source of drinking water.

Desalination has been on California’s radar since the 1960s but came to the fore in the mid 1970s, as severe drought aligned with a leap forward in technology. Industrial-scale treatment of brackish and salty water was made possible by improvements in reverse osmosis technology, a technique in which water is passed through a semi-permeable membrane to remove dissolved salts and other solids. 

Carlsbad desalination plant
Carlsbad desalination plant in March 2014.

By the mid-2000s, according to a report from California State University’s Center for Collaborative Policy, there were 16 small desalination plants – capable of treating between 2,000 and 600,000 gallons per day – supplying drinking water to communities across the state. But economics and environmental concerns have proven to be stumbling blocks to large-scale desalination, as numerous plants have been proposed and never built or shuttered outright.

Today, however, with growing populations and rapidly dwindling surface and groundwater supplies, desalination is getting a serious second look. More than a dozen desalination plants are in the planning phases along the California coast – from Santa Cruz in the north to Carlsbad in the south.

The wealthy seaside enclave of Santa Barbara, for example, is in the midst of a plan authorizing $32 million to reactivate its Charles E. Meyer desalination facility after nearly 20 years offline. The facility, which can treat 5,000 acre-feet of water per year – about 20 percent of the city’s total supply – was built after a prolonged dry period in the late 1980s. But the plant was taken offline in the mid 1990s after precipitation increased and less expensive water sources again became available.

Just outside San Diego, the finishing touches are being put on the $1 billion Carlsbad desalination plant, which, when brought online in 2016, will be capable of delivering 56,000 acre-feet annually – or 50 million gallons of water per day – to residents in the San Diego region.

Last week, the Metropolitan Water District, which serves 19 million people across the Los Angeles and San Diego metro areas, approved a plan to increase subsidies for various types of water projects, including desalination plants. “Ongoing and new efforts to locally produce these resources and lower water demands plays a fundamental role in our long-term water plan,” said Metropolitan board chairman Randy Record in a press release. "However, the costs to develop and maintain these supplies are a significant hurdle to initiating new projects.”

While desalting plants have become more efficient, costs are still high when compared with other methods of delivering water. According to data from the UC Davis Center for Watershed Sciences, costs for desalination can run between $500 and $2,500 per acre-foot compared with, say, $300 to $1,300 per acre-foot for the treatment and reuse of municipal effluent.  Most of this energy would come from the combustion of fossil fuels, which, critics note, would release  vast amounts of carbon into the atmosphere – further contributing to the state’s warming temperatures, dwindling snowpack and vanishing water supplies. 

However, Heather Cooley, director of the Pacific Institute’s Water Program, determined that the amount of energy it takes to desalinate an acre-foot of seawater is comparable to the amount of energy required to pump an acre-foot of freshwater through the aqueducts of the State Water Project – from the Delta, east of San Francisco to southern California.

Desalination also generates large volumes of ultra-saline brine, which must somehow be disposed of. In Saudi Arabia – where desalination provides as much as half of the country’s water supply – outfalls from de-salting plants dump brine directly into the ocean and have been blamed for increased salinity of the Arabian Gulf and degradation of coastal ecosystems. (To minimize impacts, the Carlsbad plant’s permit requires the facility blend its brine in a five to one ratio with seawater before discharging it back to the ocean.)

Beyond the immediate environmental and economic concerns around desalination are serious issues of scale. In spite of calls for desalination to replace water imported from elsewhere, it’s clear that a large-scale transition to desalination would have profound impacts on the coastline of southern and central California. “To replace half of the water Metropolitan Water District gets each year from the Delta,” wrote Nancy Vogel, a spokeswoman for the Department of Water Resources, “would require construction of approximately a dozen plants the size of the Carlsbad facility in the MWD territory – about one every 13 miles along the coast from Malibu to San Diego.”

As California’s coastal communities push into what seems to be an increasingly water scarce future, will they be forced to don this albatross to meet their water needs? Or can California’s push for efficiency and more careful monitoring of its surface and groundwater boost supplies, and make large-scale desalination unnecessary?

Jeremy Miller is a contributing editor for HCN.

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