People in less developed countries have a really hard time finding water that is suited for drinking. In order to clean dirty or salty water one could use a variety of methods, one of which would be to boil water from a container and condense it in another vessel. This way one would get rid of salt as well as dirt and/or toxic minerals in the water. A free method of doing such a thing would be using the power of the sun. Parabolic reflectors are already used in energy generation, where a boiler full of water is heated up so much that the water inside it goes to a boiling point.
Such reflectors use highly efficient mirrors to focus the energy of the sun into a single location. Mirrors like that are not cheap and are certainly not available in places where potable water is a scarcity.

My idea is to use CDs as mirrors and arrange them in a parabolic shape such as to concentrate the sun beams onto a container full of dirty or salty water.