The sun is amazing!· Did you know you can eliminate pathogens which cause water-borne diseases by placing raw water in small transparent containers and exposing them to sunlight?· This method, referred to as SODIS, is saving millions of lives in over 20 developing countries by reducing the risk of water-borne diseases.· It is definitely worth exploring the possibilities as they apply to emergency preparedness.

The sun is amazing!  Did you know you can eliminate pathogens which cause water-borne diseases by placing raw water in small transparent containers and exposing them to sunlight?  This method, referred to as SODIS, is saving millions of lives in over 20 developing countries by reducing the risk of water-borne diseases.  It is definitely worth exploring the possibilities as they apply to emergency preparedness.

During solar water disinfection the sunlight inactivates pathogens that cause diarrhea.  Contaminated water is placed into transparent plastic or glass bottles and exposed to full sunlight for 5-6 hours.  The UV-A light irradiates the microorganisms while the infared light heats the water.  If the temperature of the water rises above 45 C the synergetic effect enhances the inactivation efficiency of SODIS.  The result is safe drinking water.

Solar water disinfection will not remove chemicals, tastes, or smells.  It will not treat large volumes of water.  It requires relatively clear water.  It must have some sun to work although good results may be achieved even on cold cloudy days with increased exposure.

Solar water disinfection can be achieved by following these simple guidelines:

•  Start with a clean, small, transparent container.  Clear plastic water bottles, plastic soda bottles (1-2 liter), or glass jars with water tight lids work well.  Food grade plastic containers made from polyethylene terephtalate (PET) are preferable.  Handle bottles carefully as scratches decrease the effectiveness.  Glass works great, doesn’t scratch easily, but is breakable.  Containers that are 10 cm wide or smaller work best. 
•  Commercially produced bags and bottles are available that have a black lower surface.  The dark color induces a temperature gradient which causes the water to circulate within the container and improves inactivation efficiency.  Make your own by painting half of the bottle side black.  Exposure should occur with black side down! Similar results may be achieved by placing bottle on a firm dark surface during exposure. 
•  Fill the container with the cleanest water available. Filter turbid water through clean towels, coffee filters, or commercial filter to remove debris.  Water can be allowed to sit until particles settle to the bottom.  Pour clean water off the top into a clean bottle.    Efficiency is increased by exposing oxygen saturated water to sunlight.  Aeration may be easily achieved by partially filling bottle and shaking it vigorously.  Bottle should be completely filled before exposure.  Stagnant water from ponds, cisterns, etc. should be aerated to enhance the inactivation of microorganisms.
•  Expose water bottle to sunlight by placing the bottle on its side.  Optimal conditions with a clear, or partly cloudy sky, will produce disinfected water in 5-6 hours.  If the sky is completely covered with clouds the water bottles will need to be exposed for two consecutive days for successful disinfection.  During periods of stormy weather, alternative forms of disinfection should be used such as boiling or chemical disinfection.

Several factors contribute to the death of microorganisms and pathogens including; light, temperature, nutrition, humidity, and time.  Most pathogens cannot grow outside the human body with a few exceptions like salmanella.  This method of disinfection is amazingly simple and reliable if applied correctly.  Be sure to follow these simple guidelines for successful disinfection:

• Use appropriate transparent containers on a dark surface. Concrete and other light-colored surfaces do not produce optimal results.  Exposure on dark surfaces, corrugated zinc or tile roofs, etc. increase efficiency and are more likely to insure disinfection.
• Always place bottle horizontally to maximize exposure.  Black side goes on the bottom if using painted bottle.
• Start with the cleanest water possible.
• Aerate water for optimal results.
• Expose to full sun for 5-6 hours.  Do not allow bottle to be shaded.  Exposure time may be shorted if temperature reaches 50° C.  Once 50° C only one hour of additional exposure is required.  If sky is covered with clouds expose for two consecutive days.
• Bring water indoors and allow to cool completely before drinking.

Does this sound too good to be true?  We thought so until we began researching and found significant research proving SODIS an effective way to disinfect water.  Further information may be obtained at www.sodis.ch along with links to many research studies on the effectiveness of solar water disinfection.  While this may be a little new to many of us, for others it is a way of life. 

SODIS just may be a good alternative to using iodine, chlorine, or boiling after using a good filter.  You may never need to worry about water borne pathogens again if you have a little sunshine, a transparent bottle, raw water, and understand the principles behind solar water disinfection.