Nicely done, and a fun practical demo. If you're going to be guarding against any biocontamination, though, I'd never trust any homebrew filter, or even most of the commercial ones. All it takes is one microCC with a few wiggly critters in it to make its way around all of your carbon and cotton, and you'll be doubled over wishing for death for a couple days. Remember that you have to worry about viruses as well as bacteria, and they are orders of magnitude smaller. As you brought up at the end, boiling or chem sanitization are the only ways to be sure. Chlorine or Iodine are cheap & easy to carry, and no fire needed. The filters will make it look and taste nicer after you've done that.

Thanks for the demo! Upvoted as always...