This is great idea, but does repeated exposure to the sun increase the likely hood of the plastics bottles releasing toxins into the water, possibly creating higher cancer risks?

Why are glass bottles not recommended? I would rather use a clear glass bottle than a clear plastic bottle. Even though some studies may show that water from sun-warmed PET is safe to drink, I have read that it is not a good idea to leave bottled water in the sun for an extended period of time because the plastic can break down. I don't know which viewpoint is correct, but I would rather err on the side of caution and just use glass. I also only use Pyrex cookware in the microwave -- no plastic containers of any kind.

@ Alex Orrow: Check out the global reference site for this great idea: http://www.sodis.ch - you will find a lot of information indicating that there is no risk related to this practise (in fact, it's an urban legend that water from bottles exposed to sunlight causes cancer: http://www.snopes.com/medical/toxins/plasticbottles.asp).

@Jeff Kelsey
Glass (in any form) stops UV(ultra-violet) radiation. The entire trick is to let UV kill the germs. Other materials also stop UV, so you must pay attention to what you use for exposure. PET are good

Glass filter's out UVA radiation from sunlight, that is why you dont use glass.

Check this comment at http://thereifixedit.com/2010/05/13/epic-kludge-photo-historical-thursday-sodis-solution/?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+ThereIFixedIt+%28There%2C+I+Fixed+It.%29 About the little boy in the picture.
"How fortuitous! While taking a picture of this SODIS device, a National Geographic photographer captured on film a young African sprite in pink garb that was unable to flee fast enough from the camera’s view. These rare creatures cast no shadow. They also move so swiftly and carefully that they seem to never actually touch the ground, thereby leaving no footprints or dust trails as evidence of their visit.”
What happened here, you need someone in the picture to explain that is in Africa,an pout the little boy after or yhe picture was so rettouched that lost the boy"s tracks?

Glass strongly absorbs UV-A. 'Erring on the side of caution' would leave you with non disinfected water.

The Snopes link claims it is not true that "freezing" bottles releases "dioxins." However, it is well-documented that heating different types of plastic will result in releasing endocrine disruptors such as bisphenol A into the water. This method may be better than drinking viruses and bacteria, but it is not "safe."

@ Fred Stinger: Come on Fred... Do you really think Snopes qualifies as valid scientific confirmation? Do you work for a chemical company by any chance? Maybe you sell plastic? That site you referenced is for a project run by the Swiss Federal Institute of Aquatic Sciences and Technology. Usually when someone with "science and technology" in their name tells us something is safe to ingest or breathe, it eventually comes out that it's not safe. There is no safe level across the board for dioxins. This is an area that will require more extensive study before they can confirm for us that it's not safe. Examples: DDT, saccharin, lead, etc. I commend the effort and wish there was a way to do it without using plastic. But there's no way you'll convince people that those chemicals won't leech when left in the African sun for six hours.

Most people reading this blog will have the advantage of an abundant, safe supply of water. Not everyone on the planet earth is in this envious position. Waterborne pathogens can make people very ill and kill the most vulnerable - those being the young, elderly and immune compromised. This also includes the nutritionally compromised and the starving. I am one of the blessed who doesn't have to drink water from a PET bottle left out in the sun. If I lived where the little boy in the picture lives I probably would have a choice, either drink the water from the bottle or die of thirst or from a pathogen I ingested. This article helps us understand the type of help that people elsewhere in the world need from the fortunate ones (us).