How to disinfect water
(Seen in National Geographic's recent special issue - Water: Our Thirsty World)
1. Locate plastic (or glass) water bottle.
2. Tear off the label.
3. Fill with any water source that's not too murky/cloudy.
4. Place the bottle on a piece of metal, in full sun. Do not disturb.
5. Wait six hours.
6. Drink, or store in the bottle to prevent recontamination.
This Swiss-engineered water-disinfection program is called SODIS, and their studies demonstrate that six hours in the sun will kill viruses, bacteria, and parasites (giardia and cryptosporidia) in the water, making it safe to drink. Although I assume it won't clean out other types of contaminants such as heavy metals or industrial chemicals, this method of water disinfection could still save lives in an emergency when regular tap water was not available for an extended period.
SODIS is now being used all over the (extremely poor parts of the) world to provide drinking water for people with no access to purified drinking water sources, dropping rates of diarrhea and cholera. Since over 4,000 children die every day from diarrhea, this is no small deal. In fact, according to the Swiss research team, the World Health Organisation (WHO), UNICEF, and the Red Cross have recommended the SODIS method as a way to treat drinking water in developing countries where access to fuel for boiling water is very expensive.
Interestingly, the SODIS researchers also found that, when used properly, using PET plastic bottles for solar water disinfection was safe (did not release harmful chemicals into the water).
Of course, if I needed to pasteurize water I would use my Katadyn filter, or boil it in my Sun Oven/campstove/fireplace insert. SODIS, however, looks like it is a life-saving method of water disinfection for people who are stuck without another way to clean their water.