How Long to Boil Water for Purification?

Adele Eliot, Leaf Group

Boiling water is the safest method of purification. Whether you're out camping, in a country with under or un-sanitized drinking water, or you fear your local water supply has become contaminated, boiling water kills germs and parasites. If you're travelling, boiling water for drinking can be a cheaper alternative to buying bottled water. However, it's important to know how long you need to boil it to make it safe.

Reasons to Purify Water

Untreated water describes water that might come from streams, rivers and lakes, but also water that might be contaminated by pollutants such as chemicals, oils or sewage. Naturally occurring water can contain bacteria, such as Giardia, that can cause digestive issues and, in some developing countries, potentially fatal diseases, such as cholera. Water that looks clean can still contain harmful bacteria, which are invisible to the naked eye. Therefore, it's important to purify your water if you suspect it has not been treated even if it looks safe to drink.


Boiling water is the most effective method of purifying it. To do so, you will need a heat source, such as a cooker or camping stove, and a vessel to hold the water. According to the Washington State Department of Health and the United States Environmental Protection Agency, you should bring the water to boil and keep it rolling for one minute to purify it. At altitudes above one mile, 2,000 meters, you should increase the rolling time to three minutes.


When purifying your water, you will need to check whether it is cloudy first. Cloudy water needs to be filtered before boiling so you do not ingest the debris. To filter the water, you can use household items like coffee filters, cloths, paper towels or by placing cotton at the bottom of a funnel and pouring the water through. You should filter the water as many times as necessary until it becomes clear. However, remember that you will still need to boil it before it is safe to drink as filtering does not remove or kill microscopic pathogens the water might contain.


Although boiling water is the most effective method of purification, fuel shortages or lack of a heat source might mean that this isn't always possible. In these instances, you can kill most of the pathogens using plain household bleach that doesn't contain added perfumes or dyes. You need to use a clean container and add five drops of bleach for every two liters of water. The solution needs to stand for thirty minutes before it is safe to drink. This method does not kill all pathogens in water and, while it is useful in an emergency, you should try and boil drinking water where possible.