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It’s tough, but definitely possible. The idea of desalinating seawater to make it suitable for human consumption dates back so far that Aristotle even wrote on the topic. Typically, heated seawater is put into tanks under low pressure, and as the water boils, the vapors are condensed into fresh water. Other ways to desalinate water include filtering the salt water through membranes or using electricity to filter out the salts (electrodialysis).
While scientists have the process down, there are some downsides. Heating up all that water for distillation requires a lot of energy, and although some desalination sites have power plants to harness the wasted heat, the purified water still ends up being at least twice as expensive as normal fresh water. Moreover, desalination plants are gigantic structures that can cost hundreds of millions of dollars to build.
The problem is that our need for fresh water is growing increasingly desperate. According to the World Health Organization, four out of every 10 people in the world suffer from water scarcity. And by 2025, almost 2 billion people will be living with less than the minimum amount necessary for a healthy and hygienic lifestyle. But despite the high costs, many areas are still betting on large-scale desalination as the answer to the looming freshwater shortage. More than 14,000 desalination plants are already up and running around the world. While some scientists feel the impending crisis can be alleviated through better conservation and management practices, buttressing these policies with desalination seems like the best plan we’ve got.
Comments (17)
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Don’t cruise ships do this as they “cruise”. How expensive/hard can it be if I am correct?
posted by Jonathan on 8-3-2009 at 10:34 am
I was in the Navy on a submarine and we desalinated sea water for many things including for drinking water. We used steam as our source of heat since the majority of the energy plant was steam powered. We processed the fresh water even further for things like make up water to our nuclear plant and we even made our own oxygen from the fresh water.
posted by Matt on 8-3-2009 at 10:44 am
What about large-scale evaporation techniques harnessing the sun? I can’t imagine that’s that hard.
Create a shallow but large area pool and create a bubble around it: let the sun eat up the inside (like a greenhouse) and collect water as it condenses.
posted by Alamgir Kahn on 8-3-2009 at 11:24 am
Doesn’t the whole island of Aruba do this now?
posted by Buckaroo on 8-3-2009 at 12:36 pm
Alamgir, the problem i see with that is the locations at which the water is most needed. I love your plan, but i could only see it working close to shore. The transportation and constant upkeep of the water supply in these domes would far outweigh the quantity of drinkable water collected. Also, the water can’t be collected from just anywhere. Fresh water, ok…but fresh water without disease, pollution, or the ecological damage in the area makes it that much harder to locate. The only logical place to harness the water is from the oceans or glaciers, and I’m pretty sure the latter is out of the question. Transporting the water to replenish the supply in the domes would cost an astronomical amount of resources, let alone the costs to research and build the domes.
posted by Steven on 8-3-2009 at 12:40 pm
I think I saw the trick Alamgir is talking about in “the Voyage of the Mimi,” where they shipwreck, and then there’s lots of giggles when they have to get naked to warm the captain up after he suffers hypothermia.
Using evaporation is a great idea, but impractical. The amount of water needed to sustain even a small community for 1 day would require a tank as large or larger than the land occupied by the community. And then, if it’s cloudy, there is no clean water. Factor in the required maintenance (the bubble would have to be regularly cleaned for mildew) and you’ve got yourself a very impractical idea.
The electrodialysis method is, in my opinion as an electrical engineer, the eventual long term solution to the world’s water supply problem. America is poised to begin finding cheap, sustainable, green forms of power generation, like off-shore wind farms and the like. Once we have the cheap, sustainable, green technology, we can let the third world countries without water use our old equipment.
You think I’m joking, but am I?
posted by Joel on 8-3-2009 at 12:41 pm
At the very least, maybe we could just desalinate water for use other than drinking (showers, laundry, etc.) which seems like it would require less time and energy and expense????
posted by Hyacinth on 8-3-2009 at 12:43 pm
harness the power of the sun! make a solar powered desalination plant. easy as pie! have a bunch of mirrors pointing at a metal tank full of water. create a roof to catch the condensation.. etc…
posted by kevin on 8-3-2009 at 12:50 pm
I think you may have come across some dated information. Thermal desal technologies are uncommon outside of the middle east. What is far more common is the use of membrane technology through the reverse osmosis process (See Spain, Australia, Florida, Texas, and California to name a few).
Plant size and cost comparisons to conventional supplies are hugely site-specific. In places like southern California, where conventional supplies must be transported very large distances the cost difference between desal and conventional supplies are not far off from one another.
posted by SteveO on 8-3-2009 at 2:20 pm
@Hyacinth
The problem w/ that is then you have to BUILD a separate water line to homes for showers/laundry/toilets, and that’s gonna be expensive to tear up streets, lay pipe, tear up yards, and break a new water line into each home you intend to serve.
posted by Jonny on 8-3-2009 at 2:22 pm
@Jonny
Verizon FIOS did it. lol
posted by Steven on 8-3-2009 at 3:46 pm
I live on Cayman Brac in the Cayman Islands. Sea water is treated by reverse osmosis the same way Dasani and Aquafina are treated. It costs about 4 cents a gallon (US) to have it delivered and tastes great.
posted by Patricia McMahon on 8-3-2009 at 5:10 pm
Researchers are Yale University’s School of Engineering & Applied Science have discovered a breakthrough that seems fascinating:
http://bit.ly/4eVmDZ
and…
http://bit.ly/48GVi5
and…
http://bit.ly/22OC2h
posted by jim hanny on 8-5-2009 at 1:00 am
in Florida we have a desal plant, but we don’t use it to capacity. Idiots built it in an environmentally sensitive area. Seems nobody involved realized the byproduct of all that desalination would be salt.
posted by Need More Water in Tampa on 8-5-2009 at 9:48 am
I’m not a physicist but I read somewhere that particles in water can be give a magnetic charge. Don’t know if this is true but if it is, perhaps many of the particles in water could be economically removed with magnetic energy rather than evaporation or reverse osmosis?
posted by Ed on 8-5-2009 at 2:01 pm
@Matt: The story about the admiral who turned the Navy nuclear is fascinating – one of my favorite stories involves him drinking the make-up water for the reactor for the shock value in front of some politicians.
@Joel: Nobody calls it electrodialysis in industry – it’s electrodionization. And man, is it a pain in the ass to change out the modules. Of course, RO membranes and resin are both pretty terrible in their own respect, so…
@SteveO: Most new desal plants are thermal (where it is sustainable), most of the money for new plants is in thermal desal. The problem is, every plant requires an individual who is familiar with that plant to optimize and troublesheet – knowledge from one plant doesn’t necessarily carry over to another plant, the systems are so finicky. Pain. In. The. Ass.
@Buckaroo: Aruba supplies all of its potable water through a system my company built. We’re planning another one.
@Need More in Tampa: Unfortunately, if you’re speaking of the one I’m thinking of, we built that one, too. Sorry!
@Ed: Those are ions, and that’s electrodeionization.
posted by Brian on 10-21-2009 at 8:39 pm
Troubleshoot* sorry
posted by Brian on 10-21-2009 at 8:41 pm