A solar still is a low tech. way of distilling water, powered by the heat of the sun (more precisely, the heat & humidity of the soil, and relative cool of the plastic). Two basic types of solar stills are box, and pit. In a solar still, impure water is contained outside the collector, where it is evaporated by the sun through clear plastic. The pure water vapor (and any other included volatile solvent) condenses on the cool inside plastic surface and drips down off the low point(pebble), where it is collected and removed. The box type is more sophisticated.