Solar still built into a pit in the ground
A solar still uses solar energy to distill water. A few basic types of solar stills are cone shaped, boxlike, and pit. For cone solar stills, impure water is inserted into the container, where it is evaporated by the sun through clear plastic. The pure water vapor condenses on top and drips down to the side, where it is collected and removed. The most sophisticated of these are the box shaped types. The least sophisticated are the pit types.
Solar water pasteurization uses solar energy to disinfect water. The basic pasteurization process consists of heating water up to 60-70°C and holding the temperature steady for a time period. The most heat resistant organisms will be rendered inert by a temperatures of 70° in ten minutes, 75°C in one minute, and 80°C in five seconds.
Solar water disinfection (SODIS) is another method of disinfecting water using sunlight. The basic process involves filling a clear container 3/4 with water, shaking the container vigorously for 20 seconds, topping off the container and placing it in the sun. Shaking the container allows for the water to become aerated which encourages disinfection. As sunlight shines on the container the UV-A radiation causes the dissolved oxygen to become highly reactive. This reactive form of oxygen kills microorganism directly and interferes with the reproduction cycle of bacteria. As the container warms harmful organisms are also destroyed by heat treatment. Although endorsed by the World Health Organization, SODIS is not as effective as pasteurization and the completeness of disinfection is not easily measurable.
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