They are/were called or produced by a company called Dydacks (spelling may be way off). We used to use them in our lab, but I believe they are no longer produced. I will take a look to see if there are any left. We have move to a product called an integrator strip. Which looks at temp. (you can get them for various temps.) and time. I do not think for this application they would be a viable option.

On a second note: one reason the solar method of disinfection works well, is not just the increase in temp, but the intensity of UV radiation at the middle latitudes.

Pete