How Long Must Water Be Boiled Revisited
More Articles Related to WaterThe Survival Topics article How Long Do You Need to Boil Water has generated a great deal of interest on the internet. We had the pleasure of seeing it linked from a large number of sites and there has been much discussion on the subject. I decided to dig a little deeper.
As I stated in the article, the recommended times for boiling water in order to make it safe to drink are all over the place. This alone should set some red flags in anyone’s mind as to just what the correct answer is. A number of reputable sources cite that you need to boil water for just 1 minute, and not the 3,5,10, or even 20-minutes that I have seen elsewhere:
- US Centers For Disease Control and Prevention, Treatment of Water to Make it Safe for Drinking lists 1-minute of boiling or 3-minutes above 2000 meters.
- US Environmental Protection Agency, Emergency Disinfection of Drinking Water lists 1-minute boiling time and 3-minutes when above 2000 meters.
Hitting the Boiling Point is More Than Enough
If you read the Survival Topics article you will find that even boiling water for one minute is overkill. In survival situations and areas where fuel is difficult or expensive to obtain it is vitally important that fuel is not wasted.
The correct length of time needed to boil water in order to destroy disease causing organisms is actually zero minutes. Once the water has reached the boiling point it has been hot enough to destroy organisms for quite some time.
After you remove the water from the heat source it will take another period of time for the water to cool down enough for you to be able to drink it, during which it continues to remain hot enough to eliminate pathogens.
Even at very high altitudes the boiling point of water is high enough to have eliminated the threat of disease causing organisms.
Why Boil the Water at All?
The only real reason you typically try to get the temperature of the water up to the boiling point is because you usually do not have a thermometer. When the water has reached a rolling boil, you can rest assured it has become as hot as it can get (water temperature cannot get any higher than its boiling point no matter how much heat is applied) and hot enough to destroy the pathogens that can make you sick.
Is The Water Hot Enough?
Think of the temperatures attained in the cooking of meat in order to make it safe to eat. Never are these temperatures anything like the boiling point of water. In general meats require temperatures of between 145 and 165 degrees F in order to destroy potential disease carrying organisms.
The pasteurization of milk is accomplished at a temperature of about 145 to 149 degrees F and in many areas of the world water is pasteurized at a similar temperature in order to destroy disease causing organisms. In fact, pasteurization of water at significantly lower temperatures than boiling is often prefered over boiling due to vast savings in fuel.
Solar Cooking.org writes “Heating water to 65º C (149º F) will kill all germs, viruses, and parasites. This process is called pasteurization and its use for milk is well known”
In using heat to eliminate disease causing organisms, the higher the temperature the faster the results. As water approaches the boiling point these organisms are destroyed very quickly, so that prolonged boiling is not needed. In fact, it is a waste of precious fuel resources.
My Boiling Water for Zero Minutes Experiment
This morning I did a little experiment at home, which you can easily replicate for yourself.- I filled a pan with two quarts of cold tap water.
- The pan was placed on an electric stove burner and a candy thermometer placed in it.
- The stove burner was turned on.
- Once per minute I took note of the temperature of the water.
- When the water reached a full, rolling boil I removed the pan from its source of heat and continued to monitor the drop in temperature of the water as it cooled.
I live at about 100-meters above sea level and the indoor temperature was 64 degrees. In this instance the boiling point of the water occurred at about the 10th minute at a temperature of 208 degrees F (the boiling point of water varies according to atmospheric pressure). In total, the water was
- above 149 degrees for more than 25-minutes (pasteurization)
- above 165 degrees for over 15-minutes (organisms destroyed within several minutes)
- above 185 degrees for about 7-minutes (organisms destroyed within a few minutes)
- above 200 degrees for 2-minutes (bonus, extra hot, pathogens cannot survive this high temperature)
Water thus treated with zero minutes of boiling is as safe from pathogens as you are going to get it under field or home conditions, and certainly safer than any filtering or chemical system available that I know of. You will gain nothing by boiling the water for 1-minute more, and you will be wasting fuel.
So why the 1-minute boil your water recommendation by the Center for Disease Control and others? Because the key to the whole thing is that you get your water up to a hot enough temperature. Since most people lack thermometers, they want them to be sure the water they are treating gets up to a full rolling boil – proof beyond doubt that the water has become hot enough to eliminate the problem of disease causing organisms.
Results of Boiling Water Experiment
Click on the image above to view a full size chart of the following data:
Time – Temperature F degrees
Heat Applied Phase
------------------------
8:39 start
8:40 85 degrees F
8:41 95
8:42 107
8:43 123 bubbles forming on bottom and popping at surface
8:44 140
8:45 154 pastuerization has already started
8:46 167 Start 165 Degree Mark
8:47 182
8:47:30 significant water movement at 190 degrees, over 185 degrees attained
8:48 1 195
8:48:50 full rolling boil at 208 degrees heat turned off
Cool Down Phase
---------------------
8:49 208 degrees F
8:50 205
8:51 202 Temperature over 200 degrees for two minutes
8:52 197
8:53 191
8:54 187
8:55 182 End 185 Degree Mark * 7-minutes above this temperature
8:56 180
8:57 177
8:58 173
8:59 172
9:00 168
9:01 167
9:02 165 End 165 Degree Mark * 16-minutes above this temperature
9:03 163
9:04 162
9:05 160
9:06 158
9:07 156
9:08 155
9:09 153
9:10 151
9:11 150
9:12 148 Pastuerization ends * 27-minutes above this temperature
9:13 146
9:14 145
9:15 145
9:16 143
9:17 142
9:18 141
9:19 141
9:20 140
9:21 140
9:22 138
9:23 138 degrees
There can be no doubt, this water was rendered safe to drink with zero minutes of boiling, important survival information for millions of people throughout the world.
California
What about sea water or salt water? Will water from the ocean be safe to drink after being brought to a rolling boil?
Survival Topics: Safe to drink, yes. However it will not re-hydrate you.
BC
Scott, No matter how much you boil Sea water it will still be salty. What you need to do is Desalinize it. The best way to do that with boiling water is to place a large container over the boiling pot, and a collector underneath the whole contraption. Collect the condensation in the bottom container. It Is safe and will rehydrate you.
Arizona
Excellent article set. I will forever enjoy simplifying my water purification efforts because of your work. Great site, also.
Survivial Topics - Thank you Steve. My hope is that thousands of people, perhaps millions, throughout the world save valuable resources and effort by utilizing this proven information on how long you need to boil water rather than merely following the misinformation that has been circulating for so long.
Washington
What about the newer "fast boiling" products, such as the jet boil system. It brings water to a boil in about a minute. So how do these figure into the 0 minute boil? Would you need to boil the water for a couple of minutes in these systems?
Survival Topics - Just to a boil still applies. In the time it takes for the water to cool off it will have been above the threshold for a number of minutes. Most disease organisms are destroyed immediately upon reaching a temperature that is well below the boiling point.
Missouri U.S.A.
When I was a kid growing up my uncle taught me how to make a coffee can stove. You take a coffee can emptied of it's contents in which the top has already been cut out and cut out the bottom as well. Then cut a door on the bottom part of the can about 2" by 2" and cut several holes in the top for the smoke to come out.Put some tender and stick in it and your pan on top and shazam a little stove from a coffe can.
Minnesota
I remember from high school physics class that it takes something like the same amount of energy to heat water from 33F to just below boiling as it does to bring it from just below to just above boiling. Basically, changing water's phase requires a large amount of energy. That's why you'll have hot water with little bubbles forming for so long before a rolling boil occurs. So, to continue on the fuel-saving journey, wouldn't the most fuel-efficient (yet still very safe) method be to use a thermometer to bring the water up to just below boiling, say 206F or so? if that would require a significant amount less fuel, then the weight of a thermometer when backpacking would be justified.
Survival Topics - your are correct. There is actually no need to get the water to the boiling point. However if you do not have a thermometer then I recommend heating to the point of boiling as that is proof the water has become hot enough to destroy or render inert disease causing organisms.
Democratic Republic of Congo
Thanks so much! We are rewriting our new staff orientation manual and decided the old "20 minute rule" needed to be checked into!
For long term living situation (not emergency) is boiling alone sufficient or is it also recommended to also filter. We've been recommending boiling, cooling and then filtering with Katadyne filter.
Survival Topics - bringing water to a boil, or even to lower temperature if you have a reliable thermometer, is sufficent to destroy or render inert disease causing organisms. However chemical and particulate contamination will not be removed by boiling.
While there are are a number of methods that can be used in the field to clear water of mud and fine particles, removal of chemicals is a very complex undertaking. Some very toxic chemicals can find their way through the commonly used water filters. For this reason it is important to consider the source of your water. For example, choosing to use water from a clear running stream that comes off an unoccupied hill is a more likely choice than taking water from a river that flows through populated areas.
Filtering your water will help remove some chemical contaminates, so if your water source is suspect this may be a good idea. However it is important to remember that some chemicals are more difficult to remove.
Alaska
With reference to Scott's question asking about sea water.
Everyone knows you can't drink straight sea water because the salt concentration (around 3.5%) is enough to cause renal system failure in a few hours after drinking a large amount. However, you can actually stretch your fresh water supply by mixing approximately 3 parts fresh water to 1 part salt water.
Not only would you be stretching your fresh water supply, but you'd be making better use of it. By consuming some salt, your body would be forced to hold in some of the water instead of just sweating it out. That's why back before sports drinks, athletes used to take salt tablets. So in effect, you'd be making your own sports drink and adding electrolytes to your body which will help with energy.
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Germany
This is excellent information. When hiking in the wilderness my partners will often boil water for ten minutes and more. It is difficult to carry enough fuel. We need an article like this to show everybody you only need 0 minutes of boiling to make the waters safe.