Purification of salt water
Yet one more low-tech approach to producing pure water. While specifically designed for purification of salt water, it should work with any water that needs to be purified.
This particular product stands out because it is made from locally-made pottery and some metal scrap. No plywood, plastic and such.
It is Open Source you you can build on it. All described in A Simple Solar Oven Makes Salt Water Drinkable.