The basic idea is to use heat from sun light captured in a container containing food or water to cook to heat water to pasteurize it to make it safe to drink.
Ok, well shoot this is just downright cool! And anyone can do it, you dont even have to live off grid, lol.
I played around with it myself with tin foil on cardboard instead of the mirror setup and darn it all, I was pretty impressed! Click the link below to go see all the steps!