The SODIS method of solar water disinfection is a simple method that disinfects water using the rays of the sun. SODIS stands for Solar Water Disinfection.
It is very easy to do. All you need is a PET bottle filled with the contaminated water and 6 hours of sunshine. The UV-A rays in sunlight kills all germs; bacteria, viruses, and parasites all die. If you don’t have 6 hours of sunlight you will need the PET bottle to be exposed for longer periods. If it is mostly or totally overcast there will still be enough solar radiation to disinfect the water if it is left out for two days. If it is raining then I suggest that you collect rainwater to drink. Solar water disinfection doesn’t work if the sun isn’t shining.
The PET bottles are easy to come by…many soda bottles are PET bottles. You can tell that it is a pet bottle because it will have a slight bluish tint to it…even when it is a clear bottle. Use up to the 2 liter size and only use the clear Pet bottles. Choose bottles that have as few scratches as possible and wash the bottle before use.
If the water is from a stagnant source, you can fill the bottle three-quarters of the way and shake it vigorously for 20-30 seconds to improve oxygen saturation.
If the water is excessively turbid then the water needs to be filtered before it is put into the PET bottle. To test to see if the water is too turbid, fill the PET bottle with the water and place over a newspaper article. Looking down through the water from the top you should be able to read the headline. If not you will need to filter the water.
If you take a 100% cotton material like a T-shirt and fold it into four layers, you will have a filter that will remove some of the largest pathogens and much of the suspended particulates. Use each cotton filter only once before it is disinfected. It is important that the filter is washed, boiled for 30 minutes, and then dried in the sun before it is used again.
If you are concerned about pollutants in the water then you will need to use a charcoal filter. When I say charcoal I am not talking about the charcoal briquettes that you use for BBQ, I am talking about activated charcoal. Activated charcoal can remove organic compounds such as pesticides and benzene. It can be purchased in aquarium supply stores and is a smart item to include in any survival kit.
Once the water has been disinfected it should be stored and consumed from the same SODIS bottle.
Glass can be used but isn’t recommended for use with solar water disinfection because some glass prevents ultraviolet light from reaching the water. Bottles made from polycarbonate should not be used at all because they completely block all UVA and UVB rays.
The SODIS method of solar water disinfection has the ability to provide safe drinking water to anyone who needs it. It’s only cost is the PET bottle…which are thrown away by the millions each day in developed countries. The method is being taught and used in many developing countries and is providing some peoples of the world with the first safe drinking water they have ever had.