Italian designer Gabriele Diamanti has been working on his open source Eliodomestico Solar Water Desalinator for quite a few years. He posts designs that can be made from locally-accessed materials, continually refining his desalinator.
The volume is 5 liters per day of desalinated water, with no power source other than the sun. (Present desalination technology is far-more complicated and requires a lot of inputs.) For a water scarce future, this could be a huge clean water supplier.