Question: How long do you need to boil water to make it potable (suitable for drinking)?
Answer: The reality is: 0 minutes, even at high altitudes, except for maybe Mount Everest.
Discussion: Water does not actually even need to come to a rolling boil to make it biologically safe to drink. This is just the “recommendation” in most books and other published/online sources, since folks usually don’t carry around a thermometer at the campsite to check the heated water temperature. The publications all over the internet and in published books appear to espouse boiling water from anywhere between 1 to 10 minutes, just so they can CYA.
The original source that did the research and legwork to prove this was a SuvivalTopics.com That Water is Unsafe to Drink article.
AUG 2015: The original article can be found here which lists all of its sources. The follow-up article How Long Must Water Be Boiled Revisted shows the actual data to back this claim up. You can download both original articles as a PDF, courtesty of Ron Fontaine, Copyright © SurvivalTopics.com