When all else fails look to the sun. Sunlight may be used to decontaminate water via solar water disinfection (SODIS) by using the sun’s ultraviolet emissions to kill waterborne microorganisms and is currently practiced in many third world countries.
The SODIS method consist of 4 steps.
1. Clean your bottles properly with soap and water.
2. Perform basic filtering to clarify water as needed.
3. Pour water in the bottles and close the lid.
4. Leave the bottles under direct sun for a period of time as to absorb the (UV) emissions.
This method requires the use of transparent, colorless bottles no larger than 2 liters in size and composed of polyethylene terephthalate (PET). If you attempt to use glass or other types of plastic the materials can compromise the purification process by blocking the ultraviolet light needed to clean the water. Before starting keep in mind most hand sized bottles in the US are composed of PET materials.
The time frame in which the process takes to work varies greatly based on several variables. With the water in direct summer sunlight for a bare minimum of 6 hours and a water temperature of 86° F the SODIS method becomes effective in purification. Cloudy water or colder temperatures and conditions require longer exposure by the sun. To put things into better perspective, days that have 50% to full overcast require an additional 2 days of (UV) exposure for the decontamination process to be effective.
SODIS should be a last case resort. While it has been proven to eliminate many waterborne pathogens it has not been proven to kill all of them like other purification options. Also the threads of the bottles are usually thicker in nature and as of this writing it is still unknown whether or not the SODIS method will kill contaminates caught in the threads.