With respect to boiling times at altitude, hee's a quote from [/u]Medicine for Mountaineering[u], 4th edition, p. 70., by James Wilkerson, MD

"Heat is reliable; simply bringing water to a boil provides adequate disinfection. Even though water boils at a lower temperature at higher altitudes, the boiling temperature and the time required to reach that temperature are adequate to kill miccroorganisms, including parasitic cysts, bacteria, and viruses."

He then goes on to point that milk is pasteurized at 160 F, which is also the boiling point for water at 29,000 feet ASL.

Most of the wild water I have consumed over the years has been boiled, and it has worked for me. I have never contracted any illness from water, at least that I was able to notice.