A few months ago, I wrote an article called Sodis an inexpensive method of water purification. This described a method for purifying water by using sunlight. It uses plastic bottles manufactured from PETE or glass. The UV light is what purifies the water. The heat from the sun can help. I recommend you read the article.
A new and improved method of water purification using the solar ovens and the sun has been developed by Dr. Bob Metcalf, a professor in microbiology at California State University at Sacramento.
Water Pasteurization Indicator (WAPI) is a simple thermometer that indicates when water has reached pasteurization temperature and is safe to consume. Pasteurization destroys all microorganisms that cause diseases from drinking contaminated water. The WAPI consists of a small polycarbonate tube that contains a soy wax that melts when water is heated enough to be pasteurized (65˚C/149˚F). Heating water to 149˚F kills E. coli, rotaviruses, giardia, and the hepatitis A virus.
This saves fuel by eliminating the need to boil water to ensure that the pasteurization temperature has been reached.
Instruction on how to use a WAPI- The WAPI can be used with most fuels, including wood, gas, kerosene, charcoal, but it was originally designed to work with solar ovens.
Fill your container (do not use plastic) with water, place over heat or in solar oven. Place WAPI in water with the wax filled end up. To do this you have to slide the WAPI to the end of the string so that the wax end is furthest from the washer.
This puts the wax end nearest the surface of the water. When the water reaches the correct temperature, the wax melts and falls to the bottom of the WAPI. This shows that the water has been pasteurized and is ready to drink.
Remember pasteurization does not remove dangerous chemicals. Pasteurization is not the same as sterilization and the WAPI should not be used for medical or food canning.