Filling clear plastic bottles with source water is a very simple and inexpensive solar disinfection technique. The bottles are then placed on a reflective surface, such as aluminum or corrugated iron sheets, such as a roof. Depending on the conditions, these bottles are exposed to direct sunlight for anything from one hour to two days. By irradiating water with ultraviolet (UV)-A rays and elevating the temperature to 50 degrees Celsius or higher, the Sun’s rays destroy microorganisms in water.
Solar disinfection, on the other hand, does not address chemical water quality issues such as arsenic, heavy metals, pesticides, and so on. Because suspended objects and the natural hue of water impede UV rays, it also requires rather pure water. Larger bottles over one or two liters should not be used because the amount of water that can be treated is limited. It’s also not a good idea to use it on days when it’s raining nonstop. However, it has the potential to significantly reduce the occurrences of diarrhea and dysentery, as well as the devastating public health consequences that they cause around the world.
Solar stills use the Sun’s radiation to purify water of pollutants such as salts, heavy metals, and microorganisms. These systems have been used for hundreds of years and have evolved for a variety of purposes, including seawater desalination.
In some ways, the distillation process resembles the Earth’s natural water cycle. Unpurified water is placed in a container and exposed to the Sun’s rays. The Sun’s heat generates vapor, which rises from the surface of the source water. This evaporation creates pure vapor while leaving impurities in the liquid source. The clean vapor is then trapped within the still and condensed as purified water.
The remaining unpurified water, containing pollutants, can be cleaned out of the still and dumped on a regular basis.
At the residential level, compact and even portable solar units are popular. They feature few moving parts and require less operation and maintenance.
Because solar stills are affordable and require essentially little investment or infrastructure, they may be an useful treatment option for developing countries with plenty of sunny days.
However, the power of available sunlight limits such devices, and they are significantly more successful in warm, sunny climates.
Finally, distilled water contains nearly no dissolved minerals, which can be detrimental if it is the only source of drinking water and the diet lacks an other source of important minerals.
Find out more about water contamination and water treatment here.