Distillation is the process of removing salt from water. It is done by applying a heat source to the water to turn it to vapor, thereby purifying the water. Solar distillation uses the sun as the primary source of heat. It is a relatively old technology, with the first solar distillation sill put into service in 1872 in Chile.
During distillation, impure water is exposed to heat. The heat causes the water to turn to vapor. The water vapor condenses and turns back into liquid water. The condensed water is free of salt and other impurities.
A solar sill has a few basic parts. Typically, a cover sits over a basin containing a shallow pool of impure water. Nearby is a storage tank where the newly purified water is kept. Sometimes the solar distillation sill is a separate basin, while other times it is set in a ground pit.
A basin distiller is an independent unit. It is covered with an arched glass top. The bottom of the basin is usually black or a dark color, to draw the sun's heat. The impure water turns to vapor within the basin and collects on the glass cover. The condensed water runs off the sides of the glass top into a series of gutters and collects in a storage tank below.
Solar distillation is also possible in a ground pit. A conical hole is dug in the ground and a cup placed on the bottom of it. A plastic sheet is suspended over the cup, with the low point resting directly over the cup. A small rock in the center of the plastic generally weights it, and defines the low point. Larger rocks secure the plastic above the surface. Water collects on the plastic and runs into the cup.
The fact that the technology is low-tech and uses a free resource as the primary energy source makes it a good choice for impoverished countries, and in emergency situations where standard energy sources are not available. Areas of the United States that are prone to hurricanes, such as Florida, are likely to have water distillation areas set up in case of power outages, or contamination of the water supply. The ability to produce an effective solar distillation area is also considered a necessary skill for outdoor explorers. Campers and survivalists should know how to set up a makeshift basin to collect rainwater and distill it, and should carry the necessary supplies.