Always boil any water taken from the wild before drinking it; one minute of boiling is sufficient — there’s no need to extend the time just because you’re at high altitude.

35. Always boil any water taken from the wild before drinking it; one minute of boiling is sufficient — there’s no need to extend the time just because you’re at high altitude.

Cost: You’ll need to carry extra weight in the form of a stove and fuel.

In plain terms: Any microbes capable of causing illness through water are killed within seconds at boiling temperature. Boiling for an additional minute simply provides a safety margin for any possible oversight; it isn’t necessary to prolong the process at higher elevations. If boiling isn’t feasible, use a filter or chemical purification tablets instead — each method has its own limitations regarding which pathogens they can eliminate. Even crystal-clear streams and meltwater can harbor parasites.

Benefit: All microbes that can cause disease via water are inactivated within seconds at boiling temperature. The belief that water fails to reach a safe temperature at high altitudes is a common misconception.

Evidence grade: B

Sources: Centers for Disease Control and Prevention. Yellow Book Travelers' Water Disinfection: "All organisms that may cause illness from drinking water are killed within seconds at boiling temperature" "CDC recommends that travelers boil water for a full minute to account for user variability in identifying boiling points and to add a margin of safety" "Although the boiling point for water decreases with increasing elevation, at common travel elevations the temperature needed to achieve boiling is still well above the temperature required to inactivate enteric pathogens". <https://www.cdc.gov/yellow-book/hcp/preparing-international-travelers/water-disinfection-for-travelers.html>

Notes: The same page also notes that boiling isn’t strictly mandatory: maintaining water at 60°C for 30 minutes achieves the same effect, and boiling simply offers a visible endpoint without needing a thermometer. Filters and chemical tablets each have their own gaps in pathogen coverage, so boiling remains preferable when possible. Just because water appears clear doesn’t mean it’s free of parasites — appearance alone is no reliable indicator.