Water
Adjust water boil time for altitude
Water boils at lower temperatures at high altitude, so you need longer boil times to reliably kill pathogens.
Step-by-step
Below 6,500 feet (2,000 m): a rolling boil for 1 minute kills all common waterborne pathogens.
Above 6,500 feet: extend to a full 3 minutes at a rolling boil.
Do not rely on 'just to a boil' at any elevation — the water must maintain a full rolling boil for the timed interval.
For extra confidence in remote alpine environments, use both a filter and a boil.
Filter cloudy water through cloth before boiling so heat doesn't waste on sediment.
Warning: Boiling does not remove chemical contamination — heavy metals, salts, and industrial pollutants stay in the water. Only pathogens die.
Related outdoor skills
Educational reference only. Wilderness conditions change fast — practice in low-stakes settings, take a certified wilderness first-aid course, and confirm regional regulations before you rely on any of these skills in the field.