This has popped up at Gizmag; it is called a Solar Bag. It looks like it could be option for bicycle touring.

However, while PET bottles can usually only purify up to three liters per every six hours of sunlight, the Solar Bag's makes claim that its combination of high clarity polyethylene and black polyethylene allows the device to purify 2.5 gallons (9.4 liters) in the same time-span, and that it will start working on the purification process while still being transported. These two differences could potentially save lives, making the Solar Bag project an exciting prospect, even in this early stage of development.