The WaterDonut uses the UV-radiation and the heat of the sun to inactivate germs in the water, called SODIS-effect.
Through the transparent inside the UV-radiation of the sun is able to infiltrate the water. Together with the heat it will add up to a reliable disinfection of the water.
The SODIS-effect has already been operated with half black painted PET bottles. They are placed in the sun for 6 hours, for best on a ribbed roof.
At best the water is safe to be used after 3 hours in the sun. But usually there are no ideal conditions, so 6 hours are recommended to be sure.
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