Clean water is #2 on the Millennium Project's list of 15 global challenges. (Other challenges include climate change, and population & resource allocation.) Clean water faces two challenges: first, many people live in costal environments, but only have access to saline water. Second, people in many noncostal areas have been driving local water tables deeper through overutilization. I might be able to help with the first.
I believe that water's low-temperature distilation may allow for inexpensive family-sized desalination and purification units. As anyone who's lived in the mountains can attest, water boils colder at altitude. Around 0.15atm, water will even boil at room temperatures.
Water, conveniently, is very heavy. 1' head of water produces a 0.03ATM pressure drop. If the base of a 30'' water column is at atmospheric pressure and 10 degrees C, the top will boil. Connect the tops of two such units and add a temperature differential. Water will flow.
For now, here are some academic papers on the topic. I'm aware of one large-scale plant that uses vacuum distilation, but nothing small-scale excepting individual trials.
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