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[[Image:Sodis.PNG|thumb|right|150px|Plastic bottles filled with contaminated water are placed in the sunlight ]]
SODIS is a household water treatment method which uses solar energy to destroy pathogens. 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=
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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:
SODIS is more efficient in water with high levels of oxygen. Sunlight produces highly reactive forms of oxygen in the water. These reactive molecules also react with cell structures and kill pathogens (Kehoe et al, 2001).
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==
==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.
Bottles will melt and deform if the temperature reaches 65°C.
The following issues should be considered for SODIS operation:
* '''Bottle material:''' Some glass or PVC materials may prevent ultraviolet light from reaching the water. Commercially available bottles made of PET (Polyethylene terephthalate), such as the plastic bottles in which soft drink beverages are sold, are recommended. The handling is much more convenient in the case of PET bottles. Polycarbonate blocks all UVA and UVB rays, and therefore should not be used. Glass also blocks UV rays and therefore would be ineffective.
* '''Aging of plastic bottles:''' SODIS efficiency depends on the physical condition of the plastic bottles, with scratches and other signs of wear reducing the efficiency of SODIS. Heavily scratched or old, blind bottles should be replaced.
* '''Shape of Containers:''' the intensity of the UV radiation decreases rapidly with increasing water depth. Bottles used for SODIS should not exceed 10 cm in water depth. 1-2 litre volume PET bottles do not exceed this depth when they are horizontally placed in the sunlight (EAWAG/SANDEC, 2002). PET soft drink bottles are often easily available and thus most practical for the SODIS application.
* '''Oxygen''': Sunlight produces highly reactive forms of oxygen (oxygen free radicals and hydrogen peroxides) in the water. These reactive molecules contribute in the destruction process of the microorganisms. Under normal conditions (rivers, creeks, wells, ponds, tap) water contains sufficient oxygen (more than 3 mg oxygen per litre) and does not have to be aerated before the application of SODIS.
* For turbidity levels greater than 30 NTU, the water should first be filtered through a cloth or sedimented (Sommer et al, 1997).
{{Potential_Treatment_Capacity_table
| highly=
- Bacteria<br>
- Viruses<br>
- Protozoa<br>
- Helminths<br>
| somewhat=
| not=
- Turbidity<br>
- Chemicals<br>
- Taste, odour, colour
| process=
Disinfection<br>
Safe Storage
| watcrit=Turbidity < 30 NTU
}}
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 specification==
====Operation====
[[Image:Pictograms SODIS.jpg|800px]]
After treatment, the water can be consumed. The risk of re-contamination can be minimized if water is stored in the bottles. The water should be consumed directly from the bottle or poured into clean drinking cups. Re-filling and storage in other containers increases the risk of recontamination. Non-pathogenic organisms, such as algae, may grow in the conditions created in a SODIS bottle (EAWAG/SANDEC, 2002).
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. ====Safety====There has been some concern over the question whether plastic drinking containers can release chemicals or toxic components into water, a process possibly accelerated by heat. The Swiss Federal Laboratories for Materials Testing and Research have examined the diffusion of adipates and phthalates (DEHA and DEHP) from new and reused PET-bottles in the water during solar exposure. The levels of concentrations found in the water after a solar exposure of 17 hours in 60°C water were far below World Health Organization (WHO) guidelines for drinking water and in the same magnitude as the concentrations of phthalate and adipate generally found in high quality tap water. Concerns about the general use of PET-bottles were also expressed after a report published by researchers from the University of Heidelberg on antimony being released from PET-bottles for soft drinks and mineral water stored over several months in supermarkets. However, the antimony concentrations found in the bottles are orders of magnitude below WHO [http://www.who.int/water_sanitation_health/dwq/chemicals/antimonysum.pdf] and national guidelines for antimony concentrations in drinking water. Furthermore, SODIS water is not stored over such extended periods in the bottles. ====Treatment efficiencyEfficiency====
{{Treatment_Efficiency
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* 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).
==Maintenance requirements==Estimated Lifespan====Bottles become scratched or aged by sunlight and caps should must be cleaned on a regular basisreplaced periodically.
==Cost==
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.
==SafetyCountry experiences==There has been some concern over the question whether plastic drinking containers can release chemicals or toxic components into waterUsed by more than 1,000,000 in Asia, a process possibly accelerated by heatAfrica and Latin America. The Swiss Federal Laboratories [[Image:SODIS map for Materials Testing and Research have examined the diffusion of adipates and phthalates (DEHA and DEHP) from new and reused PET-bottles in the water during solar exposureAkvo.5. The levels jpg|800px|Worldwide application of concentrations found SODIS in the water after a solar exposure of 17 hours in 60°C water were far below World Health Organization (WHO) guidelines for drinking water and in the same magnitude as the concentrations of phthalate and adipate generally found in high quality tap water.projects coordinated by Eawag]]
==Games (Dutch)==
==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==
* Alternative design of a SODIS container [http://www.youtube.com/watch?v=_k-SeaRj_QY]
==External linksLinks==
*[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)]
*[http://www.enpho.org/drinking_water_quality.htm Drinking water quality information from Environment and Public Health Organization (ENPHO)]
*[http://web.mit.edu/watsan/tech_hwts_chemical_kanchanarsenicfilter.html Kanchan Arsenic filter information from Massachusetts Institute of Technology (MIT)]
*[http://www.cdc.gov/safewater/publications_pages/options-sodis.pdf Centers for Disease Control and Prevention]
==Footnotes==
<references/>
==Acknowledgements==
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==
* 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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