How Long Do You REALLY Have to Boil Water Before It’s Safe to Drink?

How Long Do You REALLY Have to Boil Water Before It’s Safe to Drink?
How long do you really have to boil water before it’s safe to drink? The answer
might surprise you!

So how long do you really have to boil water before it’s safe to drink?

     5 minutes? 
     10 minutes? 
     20 minutes? 
     30 minutes?


The correct answer: If you actually saw through our trick question and guessed 0 minutes, you would be correct!!
Now you might be thinking “Wait a minute… how is that possible?? That’s not what I learned on Survivorman or Man vs. Wild!”  Well, as you are about to learn… it’s absolutely, positively & definitively 100% possible… with just a little knowledge!
There’s a lot of conflicting information out there regarding how to “purify” water to make it safe to drink, and it can get pretty confusing. There are chemical treatments, filters and of course the “old faithful” boiling of your water to make it safe to drink. Most of these treatments are completely viable for making water drinkable as long as you know the limitations of each method.

For this article we are going to stay away from the chemical and filtration methods of water purification and focus primarily on using heat to treat water and make it drinkable. Heat is an effective method for treating water because it eliminates (kills) the microscopic organisms that are living in that water that can make you very sick.

So how much heat? And for how long? 

Great questions! Depending on your source, “conventional wisdom” has told us for decades that bringing water to a rolling boil at the very minimum and holding it there for a period of time is what is required to kill these microscopic pathogens.
For example, let’s take a look at what the Boy Scouts of America say about treating water:
The surest means of making your drinking water safe is to heat it to a rolling boil—when bubbles a half inch in diameter rise from the bottom of the pot. While this is a simple method, it does require time and fuel.”
Now let’s take a look at what the United States Marine Corp. recommends for treating water:
“Purify all water obtained from natural sources by using iodine tablets, bleach, or boiling for 5 minutes.” 
So are the Boy Scouts of America and the Marines wrong? No. Bringing your water to a full boil will absolutely kill all common pathogens that we have all learned to take so seriously because can make us sick with illnesses like Giardia, Cryptosporidium, E. coli and the rest. The problem with bringing your water to a boil, as you are about to learn, is that doing so is actually complete overkill when it comes to treating water for harmful microbes! Boiling your water, while completely safe and will absolutely kill those nasty pathogens, is actually a waste of precious fuel/firewood resources in a survival situation!

OK, so how much fuel are you wasting exactly?

Did you know that heating your water from 200° F to 212° F… just that last extra 12° to get your water to it’s boiling point… actually uses TWICE as much fuel as it does just to get your water to that initial 200°?? Well… it does. TWICE as much fuel! That is nothing to scoff at!
So now that we know what the Boy Scouts of America and the Marines say about purifying water (and we love both of these organizations!), let’s see what science tells us about using heat to purify water.

Important Temperatures to Factor In to this Equation:

212° F = Temperature at which water boils
160° F = Temperature at which milk is generally pasteurized
149° F = Temperature at which Hepatitis A is quickly killed
140° F = Temperature at which bacteria (V. cholerae, E. coli and Salmonella typhi) and Rotavirus are quickly killed
131° F = Temperature at which worms & protazoa cysts (Giardia, Cryptosporidium and Entamoeba) are quickly killed
As you can see from the temperatures listed above, the pathogens that we are primarily concerned about when it comes to safe drinking water are ALL killed (quickly) at temperatures much lower than 212°, the temperature at which water boils. That being the case… why would you unnecessarily waste any more fuel than you need to heating up your water those additional 63°? Great question, isn’t it?
Now let’s take another look at that milk pasteurization temperature above: 160° F.
Pasteurization is a process invented by French scientist Louis Pasteur during the early nineteenth century. Pasteur discovered that the pasteurization process made it possible to heat the milk to high enough temperature to kill all harmful microorganisms without “cooking” the milk causing it to curdle.

Now of course you never have to worry about your water curdling, but an important lesson can be gleaned from this milk pasteurization process that can be extremely beneficial: Water, like milk, does not have to be boiled to be safe to drink!

Temperature + Time = Pasteurization

Pasteurization is a process that occurs based on two variables: temperature and time. You see… you can actually pasteurize water at lower temps if you do it for a longer duration. This is extremely helpful in situations where A) you aren’t able to effect fire for heating your water, or B) you can make fire but you do not have a suitable container for boiling that can withstand the intense heat of your fire. Lower temperature/longer duration pasteurization can actually be done with discarded plastic 2 liter bottles set in the sunlight for longer periods of time (typically 6 hours). This method of disinfecting water is known as the SODIS (Solar Water Disinfection) method. You can even put something black or reflective behind your bottle to speed up the process!


So Why Do So Many Advocate Boiling Your Water?

Great question with a very simple answer: When those bubbles start to roll in your container of water, that is nothing more than a clear VISUAL INDICATOR that your water has become hot enough (actually MORE than enough) to have killed all of those little nasties. It works. It’s effective. But is it ideal? Or can we do better?

A classic WAPI in the author’s hand for sense of scale. Notice the bright
green plug of wax in the clear tube? That’s the stuff that melts and and
falls to the other end of the clear tube to let you know that your water is
pasteurized and ready for drinking!

Your Pasteurization Friend: the WAPI!

So if the bubbles from boiling water gives us that terrific visual indicator to let us know that our water has reached 212° F… but now we know that boiling our water to make it safe to drink is actually a waste of precious fuel resources (fuel, wood, candles, etc.)… how can we then determine if our water has gotten hot enough to have been properly pasteurized without those rolling bubbles? Great question again! We could certainly use a thermometer… but most of these are glass and very fragile. Too fragile to keep from breaking inside your kit. We need something small, light, compact, durable and can be used over and over again to let us know that our water has reached that effective pasteurization temperature. SOLUTION: A tiny inexpensive device known as a Water Pasteurization Indicator (WAPI)!
WAPI’s are incredibly simple little devices. They are nothing more than a tiny sealed clear tube with a special brightly colored (easy to see) green wax inside of them. This wax (known as Myverol 18-06) is formulated to melt at just the right temperature for pasteurization (156° F or 69° C.). In most WAPI designs the tube typically slides up and down a thin cable with a tiny weight on each end allowing you to flip the tube so that the wax inside can be easily positioned at the top of the tube again.
To use your WAPI simply slide the little tube down to the bottom of the wire so that the wax-heavy end of the tube is oriented toward the top of the tube. Place your WAPI tube into your container of water draping the weight at the opposite end of your WAPI tube over the lip of your container so that it is easy to grab. Once your water has reached pasteurization temperature of 156°, the wax in your WAPI tube will start to melt allowing it to fall from the top of your clear tube to the bottom of your tube with a little help from gravity. This is your visual indicator that your water has been pasteurized!

While WAPI’s are extremely inexpensive to purchase (typically $5 to $8), it is possible to make your own WAPI! We have even seen versions made from drinking straws and glue sticks for hot glue guns. While you can make your own WAPI, they are so inexpensive that we recommend purchasing one. “Quality control” can be an issue with DIY WAPI’s causing inconsistent results… even when purchasing DIY kits made with genuine parts. Sometimes it’s just best to leave work like this to the experts… especially when a piece of kit like this is so inexpensive to begin with.

Get your own Water Pasteurization Indicators (WAPI) here!



When traveling to countries that are known to have a questionable water supply (due to harmful pathogens remaining in the water supply), one little known trick when you cannot access bottled water is to pour yourself a glass of HOT water from the tap instead of cold. Water from the hot water heater has actually been pasteurized! Water from hot water heaters is typically between 120° F and 140° which is slightly below ideal pasteurization temperatures… but remember that heat + time = pasteurization! 99.999% of water borne pathogens are killed instantly when water is brought to 149° F. The same result can be accomplished with lower temperatures if you simply allow the water to remain at that temperature for a longer period of time. For example, water can be pasteurized at 130° F if simply held at that temperature for 2 hours.



As with anything else, use common sense when treating water. Your health and potentially your life are on the line. When in doubt, heat your water a little hotter or for a little longer. It can’t hurt unless fuel is at an absolute premium.

Just like with boiling, pasteurizing is not a panacea for making any water drinkable. For example, pasteurizing sea water will not make it drinkable as pasteurization does not remove the salts from sea water. Just like boiling, pasteurization only kills microorganisms that can make you sick. It does not remove chemicals, metals, pollutants or other toxins that could harm you from your water for you.
One example in particular that comes to mind where both boiling and pasteurizing water can make matters worse for you instead of better is in the case of the recent algae blooms in the Toledo area. Water of this type contains the toxin known as microcystis aeruginosa. Microcystis aeruginose is a species of freshwater cyanobacteria which can form harmful algae blooms (HABs) in fresh bodies of water. Boiling or pasteurizing water of this type actually INCREASES the presence of the toxins and makes your water more toxic to drink!

So when it comes to treating water to make it drinkable, be smart. Be careful. Play it safe. Use your noggin.

Happy pasteurizing and safe hydrating!

Want to learn more about Water Pasteurization? Check out our Water Pasteurization Pinterest Board!:

Follow EQUIP2SURVIVE’s Water Pasteurization board on Pinterest.

Author: Josh Nieten

Share This Post On


  1. What I know is thet you have to boil water for about 5 to 10 minutes. That was very informative. Thank your for posting this.

    Post a Reply
  2. This comment has been removed by a blog administrator.

    Post a Reply
  3. Thanks for reading, Tedd! Actually, as you can see in the article, the "required" 5 to 10 minute boil on water to make it drinkable (potable) in a survival situation is actually a myth. Water only needs to reach a temperature of 160 F to safely kill all pathogens. Arguably you could even get away with a lower temperature (like 142 F) but 160 is the industry standard pasteurization temperature. Boiling is merely a visual indicator that your water has reached 212 F (WELL past 160 F) but once your water hits a boil you do not need to continue to boil your water for 5 – 10 minutes to make it safe to drink. That is complete overkill.

    Post a Reply
  4. Very informative and educational. Here is my opinion. Most people don't have a thermometer with them. So bringing it to a boil is definitive. Better safe than sorry.

    Post a Reply
  5. Thanks DaddyDuck! You make a great point. Better safe than sorry indeed! And bringing your water to a visible boil is absolutely a terrific visual indicator letting you know that all pathogens and organisms are indeed dead and your water is safe to drink.

    That being said, there are scenarios where bringing water to a complete boil could potentially put you at risk. Understanding that a visual boil is not required to make water safe to drink is simply additional knowledge/context that can help you make potable water even when fire isn't an option or a suitable container for boiling isn't available. For example, if you aren't able to create fire because of super wet conditions or if you find a plastic container to hold your water but it is of a material that can't stand up to being placed in over a fire, you can use this pasteurization method to make water potable without having to boil it. This could be a game changer!

    For example, you could fill a 2 liter soda bottle with water and set it in the sun with a mylar blanket behind it to make it potable when fire is not an option.

    By all means, when fire is available and you have a suitable container for boiling water, absolutely bring it to a boil! We are just big advocates of "the more you know". Having a deeper and more comprehensive understanding of what really makes water safe to drink is an enormous asset and makes you more versatile when it comes to a critical skill like procuring drinkable water.

    In terms of people carrying a thermometer in their kit, we have another great article about using cheap "turkey timers" as water pasteurization indicators that you should check out! These little guys are cheap (often free!), light, compact, re-usable (most people don't know that) and work terrifically as WAPIs. You can find the article here:

    Thanks for reading and for your great comment! 🙂

    Post a Reply
  6. Drinking hot water from the tank is not safe. They are treated to not rust and release a carcinagine into the water now for cancer

    Post a Reply
  7. Thanks for the reply @Michael Reuser!

    You have a point there. There is indeed information out there validating your point, but on the other side of this equation… that information is for regular consumption of water from hot water heater tanks, not occasional consumption in emergency situations. Getting cancer from drinking water from hot water tanks would be after prolonged use, not just occasionally in an emergency.

    Hot water tanks and even toilet tanks are terrific sources of fresh water in emergencies. They are free of the biological contaminants you see during a typical water crisis like floods, algae bloom contamination, etc. (assuming you turned your main water shut off off so no contaminated water has entered your system).

    So yes, there can potentially be a risk from prolonged consumption of water from a hot water tank, but in a short term survival situation (or even a brief visit to a foreign country where you don't want to get sick from the local water), drinking from the hot water tap is preferable to getting sick from the water.

    Thanks again for your feedback!

    Post a Reply

Submit a Comment

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.

E2S Logo Abbreviated