Lets see...Ill bet its something like this:
Water is fed into a container with some kind of covering that allows sunlight to heat the water inside. As the water eveporates, it condenses on the inside of the cover, then the condensation either runs into the pond or is put into another container for later use
Dissolved solids (salts) do not evaporate. As the water in the container evaporates, the dissolved solids are left behind. The water vapor that condenses on the inside of the cover is pure and free of dissolved solids. It all sounds like a lot of work to me, but Im sure someone has a decent set of plans to build something that would work quite well. The boy scouts are tought to use a plastic sheet setup like a tent over a puddle of water to get drinking water from unclean sources. The sun does the rest.
I almost dated a psychic.....
She left me before we met.