Solar Disinfection of water, also known as SODIS, is a method that uses sunlight to purify water in glass or plastic PET bottles. The method purifies water in anywhere from six hours to two days, depending on the degree of cloudiness in the sky and the turbidity of the water. It is highly regarded for its ease and low-cost, and for these reasons has been implemented in developing countries as a safe, effective method of water purification.
But how safe and effective is it?
The main argument against this method of water disinfection is the use of PET bottles to carry it out. Some claim that it is dangerous to drink water from a plastic bottle that has been left in a hot car for a few hours, because the toxins from the plastic could leach into the water. According to this claim, over time this method of water disinfection could become carcinogenic. Of course, proponents of the method refute this claim, regarding it as perfectly safe. After all, even if SODIS is toxic over time, it is saving lives in the short run, preventing diarrhea in residents of developing countries where gastrointestinal illness from poor water quality can be fatal.
The effectiveness of the method seems questionable too. On cloudy and rainy days, it takes longer to purify the water. If the water is too turbid, it must be filtered first. However, many filters that are available to developing nations do the work of purification as well, rendering SODIS unnecessary. A fairly recent youtube video demonstrates how to purify water using the SODIS method:
(Since when do people in developing countries have access to youtube?)