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Sterilizing Water with Solar Radiation
Sarah Rich, 1 Apr 06

Watfill1.jpg In too many parts of the world, water is as much a cause of death as a source of life. Cleaning contaminated water is mass quantities presents innumerable challenges. Filtration and pipe systems can be unreliable and costly. But one innovative technique has recently proven surprisingly effective, and remarkably simple.

In Tanzania, villagers have been placing plastic water bottles full of dirty spring water in the sun on their black tar rooftops. After eight hours (or less in very hot areas), UV rays and heat have killed off the bacteria that cause cholera, dysentary, and typhoid.

The water bottle approach has benefits beyond the reduction of digestive illness. Most villagers sterilize their water by boiling it, which is taxing, time consuming, and sometimes dangerous, requiring trips into the bush to gather wood. Additionally, the open fires cause respiratory troubles and eye irritation. (Though I do wonder about about the health hazards of the melting and leaching of the plastic as it gets heated repeatedly atop a hot surface.)

What remains one of the greatest impediments to wider adoption of this approach is simply education and information. According to an organizer from Plan International (as mentioned in this BBC article), many villagers fear that the water bottles may not be an effective means of cleaning water, or may be vulnerable to further contamination when left sitting on the roof.

This news coincided with the March 22 observance of World Water Day, a global event established by the UN in 1992 to draw attention to the crisis of clean water access, and to call individuals and organizations to take action for change. One of the notable innovators for the cause is WaterPartners International, who among other things, created a WaterCredit Initiative which offers microcredit programs to help communities empower themselves to meet their own water needs locally.

For all its potential problems, though, the method does seem to have a lot to offer - it's very inexpensive, and can be implemented by anyone, anywhere that the sun gets hot enough to kill potential contaminants. It's also spurring a new demand for the collection and distribution of plastic bottles.

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I actually thought that just putting water in sunlight for a day decontaimanted it? I didn't know the heat had anything to do with it as much that solar radiation through a clear plastic bottle filtered out bacteria naturally. I was also under the impression this lowered the mineral content of water hence was used in japan to reduce the amount of mercury in the water, although I don't know, ya know? =)

Posted by: andrew on 1 Apr 06

what about the antimony from the bottles you guys wrote about Amy Smith a little while ago, her $0.05 solution (those awesome water bags with built-in spouts)is really much better than reusing (probably not cleaned that well) PET bottles

Posted by: lee schnaiberg on 2 Apr 06

This web site provides simple yet detailed instructions on the solar water sterilisation method.

In travel to Ethiopia recently one thing I noticed was that many people do not have access even to PET bottles. The price of bottled water is too high for many people, so there simply aren't enough empty bottles floating around, so those that we had were in high demand - people in several places asked us for our bottles.

Posted by: David on 2 Apr 06

This sounds promising and really easy and accessible to all, but as with all things, I'm sure many people will question exactly how safe and efficient this method is. I certainly hope we hear more about this, as well as other safe, easy, and inexpensive water sterilization methods.

Posted by: Lynn on 3 Apr 06

We have developed a high-output solar cooker that allows users to pasteurize 40 liters of water in 3 hours. Pasteurization means heating to 68 degrees, and we have a special plastic indicator which shows when this temperature is reached. Sterilization is done by boiling the water, and this is really only necessary if you are going to do surgery on somebody. Pasteurization is done to almost all milk worldwide, and saves 40% of the energy as opposed to Sterilization. It was proven scientifically 150 years ago...

Nevertheless, the Sodis method mentioned above does not even reach pasteurization temperatures and will therefore not be completely safe. It will kill most pathogens, viruses and bacteria but you have no indication that it has and such is a bit flakey.

Posted by: Jon Bøhmer on 7 Apr 06



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