THE SODIS WATER DISINFECTION METHOD
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SODIS stands for Solar Disinfection known as the solar water disinfection process. In short, the intense ultraviolet radiation from the sunlight shining through a nonopaque container filled with nonpotable water will irradiate and kill undesirable pathogens rendering the water safe to drink.
SODIS does not completely sterilize water of all critters, as it's primarily used to inactivate the pathogenic microorganisms that predominatly cause diarrhea. When the SODIS bottle is exposed to the sun, other harmless bacteria present in the water may keep growing. The SODIS method does not produce sterile water, as drinking water does not have to be sterile.
In a nutshell, the SODIS method involves filling up a clear, plastic, one- to two- quart container with nonpotable water. This bottle is then put into direct sunlight, on the roof of a house or elsewhere, for several hours until the ultraviolet radiation from the sunlight disinfects the water for drinking. More info on the subject can be found at the SODIS website at www.sodis.ch/ .
Concentrated sunlight is the name of the game so stay away from large containers with more then one- or two- quart (one liter) capacity. Don't use large containers.
Although clear soda bottles are not optimal for the SODIS method as they have a small area for exposure to sunlight, they are common and readily available in most places. Use only newer, clean, clear plastic containers with lids. Old, dinged, colored, tinted, opaque or scratched up ones will block UV radiation but they can be used to store disinfected water.
The best container to use are quart or gallon sized ziplock freezer baggies filled then laid flat as this offers more surface area and a thinner area for the UV to penetrate. Do not place the bags or bottles on top of flammable material such as hay or dried leaves and grasses as it can act as a magnifying glass and set fire to the material around it. Place it in a place that will receive full sunlight during the peak time of the day and not in a place that will be shaded during those times. The bottles should be laid on their sides increasing the area of exposure.
The water should be filtered of particulates prior to the SODIS treatment as they will impede the UV's ability to penetrate and kill harmful pathogens. The SODIS method can render microbiologically contaminated water that has been in contact with human feces potable.
The bottles/baggies need to be exposed to full sunlight for 6 hours in up to 50% cloudy skies to ensure the water is biologically safe. If it is from 50% to 80% cloudy allow them to sit for an additional 2 hours, if up to 100% cloudy then allow them to sit for 2 consecutive cloudy days. During days of continuous rain, don't use SODIS, as it's not reliable. SODIS does have a few limitations. It doesn't work for treating large amounts of water in one container and it requires suitable weather conditions for effectiveness.
The person responsible for disinfecting the water should take the job seriously, screw up this one, especially with limited medical help after a crisis, and you could help slowly kill yourself or a loved one from dysentery.
