Purifying water in the world 
Compiled by Walter Sorochan

Posted July 02, 2011

The idea is bozo simple. Put water into a clear plastic bottle. Shake it up well to oxygenate it. Put it out in the sun. The combination of six hours in the sun heat, the oxygen plus the solar UV kills diarrhea and other germs. No chemicals, low tech and inexensive!  Just common sense.

Polluted drinking water: Millions of people become sick each year from drinking contaminated water. Approximately 4 billion cases of diarrhea are reported annually, of which 2.5 million end in death. Every day around 6000 children die due to the lack of safe drinking water.

Children are especially susceptible. An estimated 1.5 billion cases of diarrhea occur each year, resulting in the death of nearly 2 million children. Worldwide, about 1.3 billion people do not have access to safe drinking water, including nearly half the population of sub-Saharan Africa. Aristanti:SODIS – Solar Water Disinfection


Developed by the Swiss Institute for Environmental Science and Technology (EAWEG), the method, called solar water disinfection, or SODIS, uses the sun’s UV-A rays and heat to decontaminate water. The disinfection method they advocate involves filling a transparent container with contaminated water.  So far, up to two million people in 20 countries have used it, though Benin is one of the few West African countries to trial the method. Irin: Sunshine makes clean water

sodis The SODIS method is more straightforward. Users take a clear plastic bottle with a maximum size of three liters, fill it with water and put it on the roof or a corrugated iron sheet to soak up the sun’s rays. Between six hours and two days later, depending on the strength of the sun, the water should be purified. Irin: Sunshine makes clean water

According to officials at EAWEG, the sun’s UV-A rays kill the pathogenic organisms in the water while its heat has a pasteurizing effect. The combined effect can kill up to 99.9 percent of the micro-organisms that cause cholera and diarrhea. Irin: Sunshine makes clean water

The chart below indicates the temperatures at which the most common waterborne pathogens are rapidly killed, thus resulting in at least 90 percent of the microbes becoming inactivated in one minute at the given temperature. (The 90 percent reduction is an indicator frequently used to express the heat sensitivity of various microbes.) Thus, five minutes at this temperature would cause at least a 99.999 percent (5 log) reduction in viable microbes capable of causing disease. (Significant inactivation of these microbes actually starts at about 5°C (9°F) below these temperatures, although it may take a couple of minutes at the lower temperature to obtain 90 percent inactivation.) Metcalf: kill water germs

MicrobeKilled Rapidly At
Worms, Protozoa cysts (Giardia, Cryptosporidium, Entamoeba)55°C (131°F)
Bacteria (V. cholerae, E. coli, Shigella, Salmonella typhi), Rotavirus60°C (140°F)
Hepatitis A virus65°C (149°F)
(Significant inactivation of these microbes actually starts at about 5°C (9°F) below these temperatures, although it may take a couple of minutes at the lower temperature to obtain 90 percent inactivation.)

Problem with SODIS: One problem in this method is it's current reliance on plastic bottles. When the plastic these bottles are made from (Polyethylene terephthalate) react with the heat & UV radiation from the sun, chemicals in the plastic can be absorbed into the water. Another problem with the use of plastic bottles is the threads in the cap and spout of the bottle. This is one spot on the bottle that can not be disinfected by the sun because the cap is covering it! So if the bottle is used to scoop up water from a dirty source, and then disinfected with the SODIS method, the water will only be re-contaminated by the threads of the bottle once poured out. It is important to keep in mind of any possible points of recontamination (i.e. dirty hands, dirty containers).  Ensminger: Caution - SODIS not totally safe 

Additional application: Solar Water Disinfecting Tarpaulin

olsen trapulin
Olsen: innovation clean water

olsen tarpafrica
Olsen: innovation clean water


ClimateLabBeta, "Solar Water Treatment," ClimateLabBeta.  ClimateLab: safe water

Ensminger Karl , "Uv water treatment," June 8,2010.  Ensminger: Caution - SODIS not totally safe

Irin, "BENIN: Sunshine + plastic bottle = clean water," Irin,July 10, 2008.  Irin: Sunshine makes clean water

Metcalf Bob, "Water pasteurization," Waikia, Metcalf: kill water germs

Olsen Eric, "innovative design of an easy-to-carry device for transporting and purifying water," Bustler,   Olsen: innovation clean water

Waters Ilana, "How to Purify Water when Traveling Overseas," eHOW, January 13, 2011.  Walters: Purifying water when traveling