I use chlorine dioxide which in theory takes 15 minutes, I make sure I give it about 30. I don't have cyst issues where I am. My normal routine is similar to WD's, dinner and tea is of course, boiled, so I use untreated water for that. During the day I will often tank up mid day because I only want to carry about a litre. Usually I stop before I am dry, down the contents of my bag and have a break while I fill and do the aquamira/pristine thing in the contents of my water bag. I then pack up the bag and be sure I've waited a while before my next drink.. never had any issues.