Yellowstone has a bunch of hot springs with varying temperatures and varying colors in the background. Many of these colors come from bacteria, we were surprised to learn. The clear pool, we heard, was more or less bacteria-free, because it was hotter. The magic nuber for pathogenic bacteria to be killed off was 180 F.

I'm thinking virii and bacteria should be pretty much done it before water gets to a rolling boil, BUT, nasties like Giardia cysts, can take longer. Spore coats on some beasties are why autoclaves became popular. These coatings are very tough and hard to breach.

CM