Is Boiling the Best Way to Purify Water?

If done correctly, boiling is a simple and effective way to kill harmful bacteria, viruses, and parasites. But boiling will not remove things like oil, calcium, lead, mercury, or fluoride from water. 

Purify water by boiling

Tap water in the United States is generally very safe to drink, but you may find it necessary to decontaminate your drinking water if 

  • You enjoy camping
  • You travel outside the country
  • Your community experiences an emergency

Why would you need to boil your drinking water?

If your drinking water is at risk for biological contamination, like wastewater, you may be exposed to pathogens (harmful microscopic organisms, or germs) like:

  • Bacteria (such as E. coli or shigella)
  • Viruses (such as adenovirus and rotavirus)
  • Parasites (such as Balantidium and giardia)

These germs, and others like them, can cause serious illnesses such as 

  • Stomach cramps
  • Nausea
  • Diarrhea
  • Bloating
  • Fever
  • Dehydration

Illness could last days or even weeks. Children, the elderly, and those with a compromised immune system are especially at risk of illness and hospitalization. 

Bottled water vs filtering vs boiling for clean water

Bottled water is one safe option for clean drinking water, but this can get expensive and contribute to environmental pollution due to plastic waste. It also may not be practical if you are hiking in the backcountry and want to limit the weight you carry. 

Filtering can remove some impurities from contaminated water, but most water filters are not capable of removing germs like bacteria and viruses because they are too small. Two exceptions to this are LifeStraw and Grayl. They both have super fine filters that are capable of removing biological contaminants from water.

If you don’t already have a LifeStraw or Grayl filter, then a safe alternative to bottled water is boiling. Boiling the water before you consume it will kill biological contaminants and prevent the illnesses they cause.

Boil water advisories and municipal tap water

Your local government or health authorities may issue a boil water advisory, also called a boil notice or a boil order, to let the public know that municipal tap water is unsafe to drink due to biological contamination. They will advise their residents to boil their water before using it or to use bottled water instead of tap water until the advisory is lifted. Boil water advisories are most often lifted within 48 hours, but this can vary depending on your situation.

How Does Municipal Water Become Contaminated?

There are 3 main reasons biological contamination could affect your tap water:

  • A decrease in water pressure

Houston, Texas recently issued a boil water advisory due to a power outage at the water treatment plant which caused a decrease in water pressure. Another common reason for a decrease in water pressure is a water main break, but there are many reasons for changes in water pressure. Low water pressure is dangerous to your water supply because it could allow back siphonage. Wastewater that would normally be carried away from your home has the potential to overpower your reduced clean water pressure, thereby contaminating the system.

  • Loss of disinfection

Disinfection is one of the final steps at a drinking water treatment facility, but if your drinking water becomes recontaminated at some point between the treatment plant and your home, you might receive a boil water advisory. An example of recontamination might be flooding due to heavy rains overpowering the storm drains and contaminating the clean water systems.

  • Unexpected poor water quality

There are many reasons your drinking water could become contaminated with wastewater and require boiling to be safe. Hurricanes, earthquakes, and other natural disasters might overwhelm your municipality’s water treatment facility with wastewater, for example, and cause an excess of contaminants in the water that it would normally be able to treat.

Are private wells affected by boil water advisories?

Boil water advisories are specific to those residents who use municipal water. Water treatment facilities that supply municipal water test it regularly for contamination. If contamination is found or suspected, they may issue a boil water advisory. As a private or community well owner, you may not be affected at home by the municipal water supply, however, you might still be affected by the advisory if you or your family use municipal water at work, school, church, or other community facilities. 

Well owners are responsible for testing their own water supply regularly. The water quality of private wells is negatively impacted by flooding due to heavy rains or snow melt, or by damage to the well itself. Coliform bacteria levels in your well water might indicate that you need to boil your water until your well can be disinfected. 

Should you boil your water when camping?

Even if your campground provides a water supply, water quality can vary greatly from campground to campground. And if you are hiking through the backcountry and relying on natural water sources, then purifying your water is a must. Even if the water from the river or the lake appears clean and clear, it is full of microorganisms that you can’t see. 

Filter the water first to remove dirt and debris, then boil it to kill the microorganisms. If you do not have a heat source (such as a campfire or camp stove) to boil water, you can use chemical tablets or powders specifically made for purifying water while camping. These are usually made of chlorine or iodine. Be sure to follow the manufacturer’s recommendations for the best results. 

Should you boil your water when traveling outside the country?

If you are traveling abroad, the source and treatment of your drinking water may be questionable. Most urban areas in North America, the European Union, and Japan have safe drinking water. Research the areas you will be visiting before you travel. 

Iceland has some of the purest tap water on the planet and it is very safe. However, if you plan to visit Mexico, the tap water may have some bacterial contamination. If you have access to a stove and a pot, boil the water for safety. Otherwise, stick to bottled water. Ice may also be a concern when you travel. Freezing will not kill the germs in water, so be sure the ice is made with purified water or avoid it altogether.

How to boil water to make it safe to drink

If your community issues a boil water advisory, or if you have any other reason to suspect your water may be biologically contaminated, boiling it is an easy way to make it safe to drink.

There are 4 things to consider for you to boil water properly:

  • Clarity

Before you boil your water, check it for clarity first. If there is anything in the water that makes it cloudy, like dirt or debris, it needs to be filtered first. This can be as simple as removing floating debris and pouring the water through a clean t-shirt, paper towel, or coffee filter to remove any solids. You could also let the water sit undisturbed for a few hours and then siphon the clear water from the top to boil.

  • Temperature

To kill the biological contaminants that may be in your water, it needs to reach 212 F. Pour the water into a pot and turn the heat up high. Bubbles will begin to form on the bottom of the pot. Then the water will begin to simmer (a few bubbles will rise to the surface). Soon the water will come to a rolling boil (when bubbles are vigorously breaking the surface). If you are using a large pot full of water, it could take 10 minutes or more to reach a rolling boil. Placing a lid on the pot can help reduce the amount of time it takes to reach a rolling boil.

  • Time

Besides a high enough temperature, you also need to allow the water to boil for long enough to decontaminate it. After the water reaches a rolling boil, let it continue to boil for at least 1 to 3 minutes. 

  • Elevation

If you are at an elevation of 5000 feet or less, let the water boil for at least 1 full minute. If you are at an elevation between 5000 and 6500 feet, boil the water for at least 2 minutes. If your elevation is over 6500 feet, boil the water for at least 3 full minutes. At higher elevations, water will begin to boil at lower temperatures. Therefore you need to boil it for a little longer to compensate for the lower temperature.

What to do with water after boiling it

After you’ve boiled the water, allow it to cool before using it. Then you can pour it into a clean container for storage until you are ready to use it. 

How should you use this clean water? 

Whether your community has a boil water advisory, you are traveling, or you are camping, use the clean, boiled water to:

  • Drink – you, your family, and your pets should drink water that has been boiled and cooled; do not drink the water from your refrigerator water dispenser
  • Cook food – wash fruit and vegetables, and cook all food using the boiled water
  • Make coffee – coffee makers will not purify the water as they do not get hot enough
  • Prepare baby formula using water that has been boiled and cooled
  • Make ice – use the purified water to make ice; don’t use ice from the automatic ice maker in your freezer because freezing does not kill bacteria or viruses
  • Wash dishes – use your dishwasher only if the final rinse will reach at least 150 degrees Fahrenheit, otherwise wash and rinse dishes by hand with the boiled water
  • Bathe – showering with tap water during a boil water advisory is generally safe for adults, but be careful not to swallow any contaminated water; children may require a sponge bath to keep the water from their mouths
  • Brush your teeth – use only water that has been boiled and cooled

When does boiling not make water safe to drink?

Not all contaminated water can be purified by boiling. Do not boil your water if it is contaminated with:

  • Fuel
  • Oil
  • Fertilizer
  • Pesticides
  • Pharmaceuticals
  • Lead
  • Radioactive materials

These will all require other methods of purification.


Boiling is an easy and effective way to purify water from biological contaminants like bacteria, viruses, and parasites. Making safe drinking water will come in handy in an emergency, or if you find yourself camping or traveling without bottled water. But, like all methods of purification, boiling does have limitations and it’s important to be aware of them.