An Extra Cheap Way To Get Salt Out Of Water Could Help Make The World Less Thirsty

Desalination is usually a hugely expensive and environmentally costly process, but this simple clay still just needs a little sunlight to render brackish water clean and delicious.

Finding clean water can be a matter of life and death. Globally 3.4 million people die each year due to a lack of clean water, roughly the population of Los Angeles. For about one-tenth of the world’s population, at least 880 million people, a reliable supply of clean water remains decades away.

But a clever design by Gabriele Diamanti is bringing clean drinking water—in a small way—much closer. Called "Eliodomestico," the solar still uses clay pottery, a metal basin, and sunlight to power a water desalination process that can work in the developing world. Because for a big chunk of those 880 million people, there is water nearby, it just happens to be undrinkably full of salt.

A solar still works on the same principles bootleggers used to make moonshine during Prohibition: evaporate a liquid with heat and then collect the condensation (and what’s left over). During hot days, Eliodomestico uses the Sun’s energy to evaporate un-purified water into vapor that condenses into water on the relatively cool interior surfaces of the pottery. This fresh, purified water runs into a basin below and is removed to be carried home. Salt and other contaminants are left behind.

At the moment, transforming salt and brackish water into fresh water is often expensive and energy intensive: power plants and hundreds of millions of dollars are needed to run larger desalination plants.

The Eliodomestico, on the other hand, is carried by hand and costs about $50. While the open-source design (anyone can use the schematics to build it locally) puts out just five liters per day under favorable conditions, Diamanti says the design is half the price of and 60% more productive than existing models.

For those without clean water to drink, that promises to be a much needed relief. Diamanti says he is now planning further development to run chemical tests on the water, offer the schematics to African craftsmen, and test local production and marketing of Eliodomestico.

Add New Comment


  • NEIL

    I'm thinking this thing costs much more than $50.
    I also don't understand the need for the terra cotta structure.
    It looks like a passive solar heat exchanger boiler on top heats the water and when pressure builds to a sufficient setting a poppet valve opens allowing steam into the shaded cool condenser below. Unless the terra cotta serves some other purpose that I don't understand, why does the support and shade have to be provided by heavy terra cotta? How about a simple wooden tripod for boiler support and a canvas tent around the condenser?
    The boiler fill cap should probably be on the boiler side as precious heat exchanger area is consumed by the cap on top.
    It seems attention should be placed on concentrating more sunlight on the heat exchanger top surface which could be done with a large light funnel surrounding the heat exchanger that could also be made of cloth or paper or foil or plastic sheet.
    It would be better to compare water production per day per surface area rather than comparing vapor condenser types.
    I'm wondering if a hand powered or bicycle powered vacuum pump installed somewhere in the system could be used to improve the rate of water production.

  • Cindy

    Since it's open source, someone should improve the design so that ladies no longer need to carry the purified water on their heads - especially not on that shallow bowl on which water would easily spill over. There are all sorts of injuries related to the heavy task of water fetching (hence innovations like Q Drum and Hippo Water Roller), so I feel strongly about the deliberate design that perpetuates the issue.

  • arbitrage

    My business just solved the problem and this discussion.

    Use both community and individual solutions.  Have the whole project financed and I will make the payments.


  • jack_sprat2

    The real stumbling block, Brent, is the lack of infrastructure to support the Slingshot, as well as the fact that you're dealing principally with technological primitives. (That's not at all pejorative, BTW. One need only be familiar with the early history of the USDA Field Agency program to understand just how big a deal breaker that is.) 

  • hmjjbe

    but that requires electricity, costs thousands of dollars and is a fairly complex machine containing moving parts that can break. it's apples and oranges. 

  • @brentwgraham

    I agree. Apples and oranges.

    But one per village might be easier than one per person.
    Maybe incorporate a solar panel on the slingshot?

    Could charge cell phones and power wifi all in one!