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[[Image:Sodis.PNG|thumb|right|150px250px|Plastic bottles filled with contaminated water are placed in the sunlight ]]
Solar disinfection is a simple water treatment method using solar radiation (UV-A light and temperature) to destroy pathogenic bacteria and viruses present in the water. It can be used to disinfect small quantities of water with low turbidity. Most commonly, contaminated water is filled into transparent plastic bottles and exposed to full sunlight. The pathogens are destroyed during the exposure to the sun. Users determine the length of exposure based on the weather conditions.
Other forms of batch treating and continuous treatment of water with sunlight are under development by various organizations.
{{procontable | pro=
- Very cheap, no capital costs except plastic bottle, no consumables required. <br>
- Independent from energy sources other than sunlight. <br>
- Treated water is protected from re-contamination in the bottles.<br>
- The taste of treated water is fresh, not stale or otherwise altered.<br>
- Convenient for storage and transportation. <br>
- SODIS has shown to significantly reduce diarrhoea
| con=
- Cannot be used on days with continuous rainfall.<br>
- Cannot be used to treat very turbid water (>30 NTU).<br>
- Bottles need to be replaced every 4-6 months.<br>
- Has a waiting period of 6-12 hours. <br>
- Needs to be cooled before consumption <br>
- Does not remove suspended partices of dissolved compounds<br>
}}
Exposure to sunlight has been shown to deactivate diarrhea-causing organisms in polluted drinking water. EAWAG/SANDEC (2002) describes the three effects of solar radiation which are believed to contribute to the inactivation of pathogenic organisms:
The SODIS method (and other methods of household water treatment) can very effectively remove pathogenic contamination from drinking water. However, infectious diseases are also transmitted through other pathways such as direct person-to-person contact, food, or unhygienic living conditions. Lack of sanitation and hygiene practices exacerbate the problem. [http://www.sodis.ch/Text2002/T-Research.htm Studies] on the reduction of diarrhea among SODIS users show reduction values of 30-80%
==History and social context==
The fact that sunlight can kill micro-organisms has been known for centuries and has been scientifically established.
==Suitable conditions ==
Basically the SODIS is suitable for batches of 1-2 litres per bottle. The system is not useful for treating large volumes of water, several are bottles needed for a large family.
* For turbidity levels greater than 30 NTU, the water should first be filtered through a cloth or sedimented (Sommer et al, 1997).
{{procontable | pro=
- Very cheap, no capital costs except plastic bottle, no consumables required. <br>
- Independent from energy sources other than sunlight. <br>
- Treated water is protected from re-contamination in the bottles.<br>
- The taste of treated water is fresh, not stale or otherwise altered.<br>
- Convenient for storage and transportation. <br>
- SODIS has shown to significantly reduce diarrhoea
| con=
- Cannot be used on days with continuous rainfall.<br>
- Cannot be used to treat very turbid water (>30 NTU).<br>
- Bottles need to be replaced every 4-6 months.<br>
- Has a waiting period of 6-12 hours. <br>
- Needs to be cooled before consumption <br>
- Does not remove suspended partices of dissolved compounds<br>
}}
{{Potential_Treatment_Capacity_table
The bottle can be used as a safe storage container. Requires suitable climate and weather conditions: the most favourable location is between latitudes 15° and 35° north/south; next most favourable location is between latitudes 15° north/south and the equator. PET bottles are abundant in urban areas, but may not be available in rural areas.
==Technical specificationConstruction, operations and maintenance==
====Operation====
Users are unable to determine when sufficient disinfection has taken place. Users need to organize a rotation system to ensure they always have treated water and know which bottles have been treated.
====Manufacturing====
Materials and facilities needed are:
* 1 or 2 litre clear plastic bottles (2 sets of 2 bottles per person, one set of bottles must be filled and placed on the roof each day, while the water in the other set is consumed)
* An alternative design using specially fabricated bags with a one-way valve integrating a temperature indicator has been proposed see YouTube video [http://www.youtube.com/watch?v=_k-SeaRj_QY]
* Accessible surface that receives full sunlight (e.g. roof, rack).
====Safety====
|field:extra=-
}}
====Maintenance====
Bottles and caps should be cleaned on a regular basis.
====Manufacturing====
Materials and facilities needed are:
* 1 or 2 litre clear plastic bottles (2 sets of 2 bottles per person, one set of bottles must be filled and placed on the roof each day, while the water in the other set is consumed)
* An alternative design using specially fabricated bags with a one-way valve integrating a temperature indicator has been proposed see YouTube video [http://www.youtube.com/watch?v=_k-SeaRj_QY]
* Accessible surface that receives full sunlight (e.g. roof, rack).
====Estimated Lifespan====
Bottles become scratched or aged by sunlight and must be replaced periodically.
==CostCosts==
{{Treatment_Cost
|CapCost=US$ 0-5 (*)
The cost of SODIS are very low, re-use of plastic bottles is common. According to a comparative [http://www.iwaponline.com/jwh/005/jwh0050599.htm study] on the cost-effectiveness of different household water treatment systems, SODIS is the least expensive method with an annual mean cost of US$0.63 per person.
==Country Field experiences==
Used by more than 1,000,000 in Asia, Africa and Latin America.
The Swiss Federal Institute of Aquatic Science and Technology (Eawag), through the Department of Water and Sanitation in Developing Countries (Sandec), coordinates SODIS promotion projects in 33 countries including Bhutan, Bolivia, Burkina Faso, Cambodia, Cameroon, DR Congo, Ecuador, El Salvador, Ethiopia, Ghana, Guatemala, Guinea, Honduras, India, Indonesia, Kenya, Laos, Malawi, Mozambique, Nepal, Nicaragua, Pakistan, Perú, Philippines, Senegal, Sierra Leone, Sri Lanka, Togo, Uganda, Uzbekistan, Vietnam, Zambia, and Zimbabwe. Contact addresses and case studies of the projects coordinated by the Swiss Federal Institute of Aquatic Science and Technology (Eawag) are available at [http://www.sodis.ch/ sodis.ch].
==Games (Dutch)Reference manuals, videos, and links=='''A Dutch Game'''*[http://www.legacy.laika.nl/games/game.php?id=petfles Game Solar Disinfection]
==Manuals==
* [http://www.sodis.ch/files/SODIS_pamphlet_e.pdf pamphlet] A brochure with information on Sodis.<br>
* A more extensive [http://http://www.sodis.ch/files/SODIS_Manual_english.pdf manual] is available [http://www.sodis.ch/Text2002/T-EducationMaterials.htm online] in different languages.
==Movies==
* Philippines [http://www.youtube.com/watch?v=FnjO-y8-Crw www.youtube.com/watch?v=FnjO-y8-Crw ]
* Sri Lanka short [http://www.youtube.com/watch?v=gwivMQkAcfg&feature=channel_page http://www.youtube.com/watch?v=gwivMQkAcfg&feature=channel_page]
* Alternative design of a SODIS container [http://www.youtube.com/watch?v=_k-SeaRj_QY]
==External Links==
*[http://www.sodis.ch EAWAG (The Swiss Federal Institute of Aquatic Science and Technology) and SANDEC (EAWAG's Department of Water and Sanitation in Developing Countries)]
*[http://www.cawst.org CAWST (Centre for Affordable Water and Sanitation Technology)]
This article is based on a factsheet from [http://www.cawst.org/ Centre for Affordable Water and Sanitation Technology (CAWST)], which is gratefully acknowledged.
==References==
* EAWAG/SANDEC (2002). Solar Water Disinfection: A Guide for the Application of SODIS. SANDEC Report No 06/02.
* Saladin, M. (2002). SODIS in Nepal – Technical Aspects. EAWAG/SANDEC and ENPHO.
* Wegelin, M., Canonica, S., Mechsner, K., Fleischmann, T., Pesaro, F. and A. Metzler (1994). Solar Water Disinfection: Scope of the Process and Analysis of Radiation Experiments, J Water SRT, Aqua Vol. 43, No. 4, pp 154-169.
* Wegelin, M., Canonica, S., Alder, A., Marazuela, D, Suter, M., Bucheli, T., Haefliger, O., Zenobi, R., McGuigan, K., Kelly, M., Ibrahim, P. and M. Larroque. (2000) Does sunlight change the material and content of polyethylene terephthalate (PET) bottles? IWA Publishing, Journal of Water Supply: Research and Technology, Aqua No. 1.
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