Boiling Water for Safety at Altitude
Boiling is one of the simplest ways to make water safe to drink, and it works anywhere you have a stove and fuel. At high elevations water boils at a lower temperature, which affects both water treatment and cooking times.
Why altitude changes boiling
Air pressure falls as you climb, so water reaches a boil at a lower temperature. At sea level water boils at 100 degrees Celsius, while high in the mountains it boils noticeably cooler.
Cooking takes longer for the same reason, especially for pasta, rice and dried beans.
How long to boil drinking water
Public health guidance recommends bringing water to a rolling boil for one minute. Above roughly 2,000 meters, or 6,500 feet, the recommendation is three minutes to make up for the lower boiling temperature.
Let the water cool naturally in a covered pot. Pouring it between clean containers can improve the flat taste of boiled water.
Boiling does not remove sediment, salt or chemical pollutants, so let cloudy water settle first and pour off the clear water before heating it.
Planning fuel
Boiling all drinking water uses much more fuel than boiling only for meals. If you rely on it, test your stove at home to see how much fuel one liter needs, then add a generous margin for cold weather and wind.
A windscreen and a lid save fuel, but follow the stove maker's guidance on enclosing canister stoves.