Drink me sticker for the developing world

I saw a charity that, I think, had people put 16.9 oz (.5 liter) water containers out in the sun on posts, then said it was safe to drink the water. I do not remember, but I think it took awhile, many hours.

I think it is warmth and possibly UV light that cause the sterilization effect. I think these could be increased strongly with a cheap 1-2 cent sticker applied to many containers even 1 or 2 liter containers.

The transparent sticker would be IR absorbing, and have little lensed bumps on it (or possibly a nonbumpy diffraction grating) to concentrate UV. When you think of a bump, or a diffractor, with an area 100 times the size of the focal point then that eentsy point gets 100 times more sterilizing radiation. So if UV previously did nt matter, it could contribute to water sterilization that way

The main improvement to affixing a sticker to a container and then tossing it haphazardly out into the yard is that you get to skip the process of installing dozens of tidy little semireflective posts in your yard, and can instead just fling things around haphazardly and still get drinkable water.

If the IR absorption of a container of water on a tidy reflectorized post is 20%, and that of a UV transparent IR absorbing sticker 99% then the sticker can be five times smaller than the container and get the same results, which makes it cheaper and easier to stick on. Alternatively it might mean that you can sterilize a larger 1 or 2 liter soda container at a highly similar surface area, which gives a person much more water per refill.

at 1-2 cents per sticker that would cover 1 billion containers for $10-20 million $ and prevent a lot of water based illness