Desalination is the process of taking the salt out of ocean water to convert it into drinking water. An EarthSky listener asked why desalination isn’t in greater use in U.S. coastal regions – like California – where water scarcity is an issue. As yet, no full-scale desalination plant – that is, a plant that produces millions of gallons of freshwater per day – has been built there.
EarthSky spoke to Heather Cooley, co-director of the water program at the Pacific Institute. She told us the answer is complicated. Desalination has one huge plus, she said – it relies on plentiful seawater. She said:
It’s not dependent on local climate conditions. In addition, water produced from seawater desalination is very high quality.
But, she added, desalination can have drawbacks. For instance, she said, desalination plants can cost millions to billions of dollars to build.
A lot of the cost is also in operating the facility. It’s also very energy intensive, which raises questions about the cost, but also about greenhouse gases.
Cooley explained that it takes a lot of power to run a desalination plant because seawater, in order to be purified, is typically pushed through filters, or “membranes,” at very high pressure. She said:
It’s very expensive, considerably more expensive than other water supply options, or conservation measures.
But, she said, the advantages and drawbacks of desalination will likely shift as water scarcity on Earth increases in the 21st century, and desalination technology improves.
Cooley added that desalination also has environmental impacts which aren’t particularly well understood – for example, impacts on ocean life near water intake vents.
I think a lot is not known, especially on the environmental impacts globally.
To learn more, Cooley is launching an in-depth study on desalination around the world, which the Pacific Institute plans to publish in the summer of 2012. Cooley said that she did a previous study in 2006, when plans to build about 20 desalination plants were on the table in water-scarce California. As of 2011, only one plant had opened (in Sand City, California). She said:
It’s small. Some of the ones they’re considering in Southern California are on the order of 50 million gallons per day. In some cases they’re considering some that are 75-100 million gallons per day. The one in Sand City was considerably less than a million gallons per day, considerably less. Some of the issues in terms of the bigger plants – there are a lot of groups opposing them – some of the issues are related to open-ocean intakes in particular. That particular facility in Sand City is using sub-surface intakes, which have fewer environmental impacts.
That is, the Sand City plant is drawing its water from pipes underground, and using sand as an initial-stage filter. Most of the time, desalination plants, especially bigger ones, don’t have that luxury. They have to draw their water from the open ocean, which can pull in plants and animals, and are thought to possibly disrupt the coastal ecosystem.
That’s one of the things we’re trying to tease out in our [new] analysis – why did that plant in Sand City get built, what are the concerns with the larger facilities that are being proposed.
Ground was broken for another desalination project in California, the Carlsbad Desalination project, in 2009. The plant was conceived as a facility to desalinate upwards of 50 million gallons of seawater a day, and serve residents of Carlsbad, California within the next few years. The project took ten years of planning, and five years in the state’s permitting process. There has been legal wrangling, and permits are currently poised to lapse, according to Heather Cooley. In contrast, an even larger project in Israel had a significantly quicker turnaround for approval: about a year. Water demand in the Middle East is possibly more intense than it is in the United States. As Heather Cooley pointed out:
Seawater desalination is in use around the world. It’s been most successful in areas that have very little water, like the Middle East, and very low cost of energy, again, the Middle East would be an example of that.
The majority of the world’s 13,000 or so desalination plants are located in the Middle East. Cooley added that, looking beyond money and energy, desalination’s environmental impacts offer another obstacle to their construction in the United States. She said these impacts haven’t been very well studied – impacts on marine life near ocean water intake vents, for example. Cooley said:
There are plants that have been operating for a very long time, but it’s generally in areas where environmental concerns were very low, and so there hasn’t been a lot of long-term monitoring in those particular facilities. So with some of the new plants, they are being built in areas where environmental concerns are much higher.
EarthSky also spoke with Yoram Cohen, a global desalination expert at UCLA who has worked with desalination experts in both Australia and Israel. He said the expense and slow progress of developing desalination plants in California is in part due to political, policy and other obstacles. That said, both water experts agree that desalination needs to be studied further.
Both Cooley and Cohen say desalination is not the magic bullet answer to all our water troubles. Cohen said we need to focus on what he called an “integrated approach” to developing water solutions around the globe. In other words, in some places, using more recycled water than desalinated water might work. In other cases, the balance might have to be reversed. Cooley echoed the sentiment:
It’s true in the United States, it’s true in California, it’s true globally. We have enormous water supply problems, and as population grows, as economies grow, are potentially going to become more severe. Climate change is a very big issue, and that will impact the supply and demand for water.
It’s very important that we look at all the options – I know that some people like to focus just on the technology. But we need to look at all the water supply and conservation options available and try to find solutions that are the most cost effective, have the least environmental impact, and are sustainable
Listen to the 90-second EarthSky interview with Heather Cooley on the advantages and drawbacks of desalination (at top of page).
Beth Lebwohl researches, writes and helps produce science content in audio and video formats for EarthSky. She is one of the authors on EarthSky.org, a script-writer for our podcasts, and helps host our English science podcasts in 90-second, 8-minute and 22-minute formats. Beth came to EarthSky in 2006 from the American Museum of Natural History's Department of Astrophysics, where she was surrounded by some of the greatest telescope-building, equation-wielding, code-writing physicists of our time. And they made her think . . . this science thing . . . it's pretty cool.