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A clear plastic bottle filled with water, exposed to the sun for 6 hours will make the water safe to drink (see the caveat list). In fact, the effectiveness of terminating harmful bacteria is an amazing 5-Nines, that is, 99.999 percent!
This method kills germs. If the water is already contaminated with chemicals from pollution, the chemicals will remain.
If the water is cloudy and dirty, it should be filtered first to allow the UV-A rays to effectively penetrate into the water.
The plastic water bottle should be no bigger than 3 liters. In moderately cloudy water, UV-A will lose 50 percent effectiveness at a depth of 10 mm (about 0.5 inch), whereas UV-A will only lose 25 percent effectiveness at a depth of 10 mm in clear water. Just use a typical size soda bottle or water bottle.