Boiling water in pan on electric stove in the kitchen

How to Purify Water by Boiling (& Why It Works)

People have been boiling drinking water as a means of purification for centuries.  These days, we have multiple treatments and purification processes to kill contaminants in tap water, yet, boiling water is still relevant. Most people associate boiling water with emergency contamination situations. 

However, depending on where you live or how pure you like your water to be, boiling water for water treatment might still be necessary for disease control purposes. Whether you are in an emergency situation or not, boiling water is a simple and safe way you can purify your water.

A glass of contaminated water on a table.

Drinking water may reasonably be expected to contain at least small amounts of some contaminants.

Why Would You Need to Boil Water?

The most common situation in which you would need to boil water would be in the case of a city or state-wide boil-water order.  These occur as a result of biological water contamination.  Under these circumstances, tap water that is normally safe is too contaminated to drink.  The most likely events that lead to the biological water contamination include:

  • Loss of water pressure in municipal or well water distribution systems
  • Loss of disinfection in the municipal or well water system
  • Extreme contamination of water prior to disinfection

Some of the most common causes of these events include:

  • Waterline breaks
  • Purification system breaks
  • Severe weather events
  • Power outages

In all of these events, a boil-water order is likely to be issued. Additionally, despite lengthy water purification processes, biological contamination can still happen at any time with or without a boil-water order occurring.  As a result, the EPA put forth a list of potential indicators that there may be biological contamination in the water that would make boiling water for purification necessary.  Some of these indicators include:

  1. Turbidity: This explains the cloudiness of the water.  By looks alone, if the water appears cloudier than normal, then that could indicate some type of biological contamination.  Only ever drink clear water that is see-through!
  2. Coliforms: Water highly concentrated in coliforms bacteria levels indicates that there are potentially unsafe levels of bacteria in the water.  You most likely won’t be able to measure coliform level yourself.  However, you can check in with your local government’s reporting to see how well the water performs in terms of coliform concentration.
  3. Enterococcus: Water highly concentrated in enterococci bacteria may indicate that the water has been contaminated with fecal matter.  Like coliforms, you’ll have to check with your local government to see reports on enterococci. 

In each of these three cases, biological contamination may occur with or without an emergency water declaration.  Therefore, it may be a good idea to both regularly inspect your water for any abnormalities and check in with your local government reporting. If you are under a boil-water order or your water shows other indications of biological contamination and you are unable to boil water, then you must drink bottled water in order to avoid getting sick.

How Does Boiling Water Purify it?

Boiling water kills off biological contaminants.  Biological contaminants are living organisms in water.  When ingested, they can cause diseases and make you sick. Boiling water is technically a pasteurization process.  According to the US Environmental Protection Agency (EPA), pasteurization is a process in which the organisms that could potentially cause harm to humans are killed off. 

Moreover, pasteurization does not kill off all of the water’s organisms, but rather just the ones that would be bad for human health.  On the other hand, sterilization would kill off all of the water’s organisms including the harmless ones.  When water reaches a boil, it kills biological contaminants by denaturing their proteins.  While different types of biological contaminants are killed off at different temperatures, 99% of them are killed off if heated to at least 149 degrees Fahrenheit for 5 minutes.

However, the Center for Disease Control (CDC) recommends that you boil your water at least 212 degrees for 1 minute in order to ensure its safety.  If you’re concerned that your water is highly concentrated with contaminants, then just continue to boil it past the 1-minute mark. Whether you choose to boil your water or not, it is always a good idea to make use of an at-home water filter or purifier system in order to reduce the risk of contamination.  

water boiling

Contaminants in Your Water Supply

Water contaminants, while seemingly all bad, are not always necessarily bad.  The EPA defines a water contaminant as anything in the water that is not a water molecule.  Therefore, any and all molecules in water that aren’t water are considered a contaminant. Water contaminants that are bad for human health fall into four key categories:

  1. Biological: These are contaminants that can be killed when boiling water.  They are called microbes or microorganisms as they are some of the smallest living things on earth.
  2. Chemical: Chemicals cannot be removed from water with boiling.  They include both man-made and naturally occurring chemicals.  Man-made chemicals usually make their way into the water supply either through groundwater contamination or chemicals seeping into surface water such as freshwater lakes and rivers. One of the most common man-made chemical water pollutants is chemical pesticides.  These are particularly dangerous as they often contain nitrate, a substance that reduces the body’s ability to carry oxygen through the blood.  It is particularly dangerous for children and infants.
  3. Physical: Physical contaminants are not removed from water with boiling.  They are typically visible to the naked eye.  They mostly include sediments from rivers and lakes such as clay or sand.  They are harvested with water when erosion brings the sediments up to the water’s surface.
  4. Radiological: Radiological contaminants are also not killed off by boiling.  They are a specific type of chemical contaminants that emit radiation.  They are typically released into the environment through mining activities and eventually find their way into groundwater and surface water sources.  Some common radiological contaminants include uranium and radium.  When ingested, they can increase your risk of having kidney disease or cancer.

Contaminants from each of these categories generally stem as a result of four different human activities including:

  • Agriculture
  • Commercial (air travel, construction sites, waste disposal, etc.)
  • Industry (oil and gas production, pipelines, etc.)
  • Residential (household chemicals, floor drains, etc.)

Therefore, monitoring these activities plus the natural, biological elements of our environment is essential in order to ensure water does not become contaminated.

Biological Contaminants

Biological contaminants are contaminants that can be removed from water by boiling it.  Not all biological contaminants cause poor health and many are naturally occurring in our environment.  For the most part, biological contaminants that cause health problems come from feces contamination.  We refer to these bad contaminants that cause diseases as pathogens. 

Also known as microbes, biological contaminants live all over our planet.  They even live within our own bodies to help promote good health.  Some microbes, however, can wreak havoc on health and cause different infections and gastrointestinal diseases. These pathogenic microorganisms generally fall into three categories including:

  1. Bacteria: Bacteria can cause numerous, commonly known bacterial infections including E Coli.  Another common and highly dangerous form of bacteria, known as legionella, has the potential to cause a handful of different health problems including a severe form of pneumonia known as Legionnaires’ disease.
  2. Viruses: Viruses are some of the smallest life forms on earth making them very difficult to locate and kill.  When they infect a person, they utilize the resources of that person in order to grow and multiply.  Common viruses that are found in water and known to cause harm to human health include Hepatitis A as well as different rotaviruses.
  3. Protozoan: Protozoa are common in water because they need it in order to survive.  They typically make their way into water streams through fecal contamination either from farms or households.  Most commonly, though, they come from cattle farm runoff.  The most common protozoa include cryptosporidium and giardia and both of them can cause diseases in humans.

What About Purification Systems?

Your city and home purification systems typically do a good job of removing all different types of contaminants.  However, as we’ve already gone over, contaminants can sometimes still slip through the cracks even after going through thorough purification. The most common purification methods to remove biological contaminants include:

  • Ultraviolet (UV light) treatment
  • Micron filtration
  • Reverse osmosis
  • Distillation 

Each of these treatment methods generally does a good job at killing off biological contaminants.  Additionally, having an at-home water filter can help remove some contaminants.  Most home filters are able to remove at least some bacteria and protozoa, but not so many viruses. 

Viruses are generally too small for home filters to catch.  In order to get the best filtered water at home, purchase the smallest micron-sized filter available and be sure to regularly replace it.  The smaller the filter size, the more effective the water filtration will be. 

It’s important that you’re able to rely on your city or well for clean water.  But, purifying water at home with your own filter is a great extra step you can take to ensure water safety.  Regardless of how high quality you believe your water is, this extra step can go a long way in making your water safer.  

How to Boil Water at Home for Purification

If you’re in a situation where you need to boil water for safety, then have no worries because it is simple and effective to purify your water at home with this process. Follow these steps to boil your water at home:

  1. Check your water’s clarity: Let water out of your taps and have a look at it through a clear container.  If the water looks cloudy, then you need to filter it through a physical filter to remove physical contaminants. A coffee filter, paper towel, or washcloth all work great as physical filters.  Pour the cloudy water through the filter and into another clear container.  If the water is still not clear after the first time, filter it a second or third time.
  2. Bring water to a boil: Pour the clear water into a stovetop pot and bring it to a rolling boil.  Allow the water to sit at its boiling point for at least 1 minute. Depending on how high above sea level you live, you may need to boil your water for longer than 1 minute.  As a rule of thumb, for every 5,000 feet you live above sea level, then boil your water for an extra 3 minutes.
  3. Cool water: Once time is up, turn the stove off and allow the water to naturally cool down to room temperature.
  4. Add salt: Once the water hits room temperature, add in a pinch of salt to restore flavor.  For every liter or quart of water, a pinch shall do. 
  5. Store water: Store the water in clean containers.  Your water is ready to drink!  
 The symbol Cl with atomic data and yellowy-green liquid chlorine solution in the background.

The United States first started chlorinating tap water in 1903.

If you are unable to boil water or want to be extra cautious about your drinking water, then you can also use household bleach as an extra disinfectant measure. Before getting started, you need to have a look at your bleach and check the label for a few things in order to indicate that it is suitable to use in your water.  Double-check that your bleach is:

  • Regular, unscented chlorine bleach 
  • Suitable for disinfection and/or sanitization
  • Either 6% or 8.25% sodium hypochlorite

If your bleach checks all of these boxes, then it is safe for you to use. Next, depending on the percent sodium hypochlorite in your bleach, you will use different amounts of drops in the water.  Follow these rules for sodium hypochlorite:

  • If your bleach is 6% sodium hypochlorite, use 8 drops of bleach for every gallon of water
  • If your bleach is 8.25% sodium hypochlorite, use 6 drops of bleach for every gallon of water

Follow these steps to use bleach as a disinfectant:

  1. Gather supplies: Locate a clean dropper and bleach.  If you don’t think you have a dropper, check your kitchen or first aid kit.
  2. Drop bleach into the water: Grab your boiled water and add the recommended amount of drops to your water.
  3. Let the water sit: Set your water aside for 30 minutes.
  4. Drop more bleach into the water: Once the 30 minutes is up, grab the water and repeat adding the same amount of drops in the water again.
  5. Let the water sit: Set your water aside for 15 minutes.  
  6. Test water: Once the 15 minutes have passed, feel free to drink the water.  It may have a slight chlorine taste, however, this is not harmful. 

Times You Should Boil Your Water

In addition to boil-water orders and other indications that your water may be contaminated, some other occasions call for boiling water as well.  A few of these occasions include:

  • Camping
  • Foreign travel
  • When water tastes bad

First off, when going camping, you’ll most likely need to boil water if you don’t have either a water purifier with you or are within walking distance of a campsite where water can be purchased.  Boiling water allows you to have safe drinking water after a long day of hiking and activities.  Plus, being able to boil water while camping means that you don’t have to miss out on your morning coffee!

Second, US citizens should be wary of drinking tap water in foreign countries.  Even if it has been purified, there is still a good chance that the water contains microorganisms that your stomach has never been introduced to before which could cause you to get sick.  If you don’t have a bottle of water handy while traveling, then be sure to at least boil the purified water. 

Lastly, boiling water can actually help improve the taste of the water.  While not everyone likes it, boiled water has a particularly flat taste to it.  This is so because most of the air in the water is lost while it is boiled.  As a result, the water tastes flat.  If you like particularly bland water, then try boiling your purified tap water.

Should You Try Boiling Your Water?

Regardless of how clean you believe your water is, it never hurts to go the extra mile and boil it.  Purified water, while it may look okay, could easily be contaminated with harmful biological contaminants. If you’re feeling uneasy about the safety of your water or even don’t like the taste of it, boiling could be a simple, cost-free solution.  

Bonus tip: Check out our top picks for at-home water filter pitchers for easy and reliable water purification. 

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Joshua Perkins

Joshua spent ten years as a water systems technician in California before settling down with his wife and two young children in Nashville in 2018. Through all of his experience, he learned the benefits and shortfalls of so many different types of water filtration systems, from pitchers to whole-house installations. He started Water Filter Authority in 2019 to empower other families to make the right decision for their long-term health and wellness.