The short answer
Bring water to a vigorous rolling boil and hold it there for at least one minute. If you live above 2,000 metres (about 6,562 feet) elevation, boil for at least three minutes. That single rule matches guidance from the CDC, the EPA and Health Canada, and it kills the organisms that matter in drinking water emergencies: E. coli, Salmonella, Vibrio cholerae, Giardia and Cryptosporidium cysts, and viruses such as hepatitis A.
Why one minute is enough
Water at a rolling boil is at or very near 100 °C (212 °F) at sea level. Pathogens in drinking water die in seconds at that temperature; the one-minute margin covers uneven heating, cool cups of water you might add mid-boil and thermometer-free guessing. The extra two minutes at high altitude compensates for water boiling at a lower temperature as air pressure drops.
How to boil water properly during an advisory
- Start with cold tap water — hot water sits in the water heater and can carry more sediment and dissolved metals.
- Use a clean pot or kettle and fill it no more than three-quarters full so it does not boil over.
- Heat until large bubbles roll continuously from the bottom, then start a timer for one minute (three minutes above 2,000 m).
- Turn off the heat and let the water cool covered, without adding ice, for at least 30 minutes.
- Pour into a clean, sanitized container with a lid and refrigerate. Use within a few days or reboil.
Do not rely on these shortcuts
- Kettles that switch off at first bubbles may not hold a full rolling boil for a minute — let it click off twice, or use a stovetop pot when you can.
- Coffee makers, microwaves that heat unevenly, and UV or charcoal filters are not reliable disinfection methods during an advisory.
- Boiling does not remove chlorine taste — that is normal — but it concentrates nitrate and many chemicals, so never boil water under a chemical do-not-drink notice.
Storing boiled water
Store cooled boiled water in food-grade containers that have been washed and rinsed, ideally sanitized with a mild bleach solution and air-dried. Refrigerate for drinking water and keep a smaller covered container at the sink for cooking and teeth. Label containers so nobody confuses them with unboiled water, and discard stored boiled water after 2–3 days.
FAQ
Does a rolling boil really need bubbles?
Yes — the standard is big, continuous bubbles that do not stop when you stir. Simmering water below a full boil is still very hot, but the CDC’s one-minute rule is defined at a rolling boil, so stick to the rule to be safe.
Can I boil water in the microwave?
Microwaves heat unevenly and can superheat water without visible bubbles. If it is your only option, microwave in a microwave-safe container with a stirrer or wooden spoon inside, then stir carefully and verify the water is fully boiling for one minute. A kettle or pot is better.