A Reader's Boiling Water Experiment
More Articles Related to WaterChris Smith is kind enough to share with us a boiling water experiment he performed at home.
If you recall, the Survival Topic How Long Do You Need to Boil Water stirred up a heated controversy as it challenged some long held beliefs. This lead to an additional Survival Topic entitled How Long Do You need to Boil Water Revisited where we went through an actual boiling water experiment in order to measure the amount of time a pan of water stayed above the temperature threshold necessary to destroy disease causing organisms.
In performing the boil water experiment I was making enough potable water for a day, or about two liters or quarts. However, Chris came up with a twist that I had not fully considered - namely that the time it takes for a pan of water to reach the boiling point and then cool to room temperature will vary according to how much water is in the pan and the amount of heat applied per unit of time.
Chris writes:
Nice article and accompanying experiment on the How Long Must Water Be Boiled Revisited page. There is one objection that might be made, however. Consider the realistic non-survival situation of heating a cup of water for tea or a packet of non-pasteurized milk (2 cups). Let's consider the smaller quantity of 1 cup.
Using the same apparatus that you used for your experiment, one might argue that since 1/4 the quantity of water was being used (4 cups ~ 1 quart ~ 1 liter) then all the times would be compressed by a factor of 4. This means that the time the milk was above a threshold temperature will be decreased.
I tried this and found that the cup of water in my kitchen took 4 minutes to reach boiling. It took more than 2.5 minutes (not the expected 1/4 of your 10 minutes) because the pan itself needed to be heated. Let's just say that my times were 1/2 of yours. The bad news is that the total time above threshold temperatures is approximately halved and perhaps insufficient for sanitization according to the guidelines you cite above. HOWEVER, the good news is that (according to a 1996 Journal of Travel Medicine article) the most heat resistant E. coli type bacteria do not survive for *any time* above 70 C (158 F). The same article also warns that the criteria "too hot to touch" for determining when 70 C has been reached is not reliable--10 of 15 people tested considered 55 C (131 F) water too hot to leave an index finger in for more than 5 seconds.
SO...if you don't have a thermometer and want to make sure your water is safe, do as you've said: boil for zero minutes. You will have killed the bacteria when you get the temperature above 70 C (158 F). and you will have killed (according to your citation above) the giardia at 100 C (212 F). It's a good way to save energy.
Thank you Chris for sharing this excellent information!
You are welcome to share this Survival Topic with others. I only request that you use a short blurb (not the entire survival content) and this code to
link to the origional:
