Also, I question: do you really need to boil the water?
Would 170 degrees F be OK?
I found this quote:
"According to the Wilderness Medical Society, water temperatures above 160° F (70° C) kill all pathogens within 30 minutes and above 185° F (85° C) within a few minutes. So in the time it takes for the water to reach the boiling point (212° F or 100° C) from 160° F (70° C), all pathogens will be killed, even at high altitude."
on this page of survival topics:
http://www.survivaltopics.com/survival/how-long-do-you-need-to-boil-water/Problem is you may not have a thermometer with you, hence, bringing the water to a boil to be absolutely certain. Sorry to digress, now back to your regularly scheduled topic.