Harvard Health Tips
Boiling water for purification
When the water supply is questionable, boiling is by far the most reliable method to make water safe to drink. Bring water to a vigorous rolling boil for one full minute and then let it cool to room temperature. Don't add ice to speed the cooling, because it could reintroduce harmful organisms to the water you've just purified. At high altitudes (above 6,500 feet), boil water for a full three minutes.