Water must be boiled at a rolling boil for how long to be disinfected? What do you think the correct answer is? Graphic by the Author
So, on the question
above, what answer did you pick?
Did you know that all of
the answers above have been recommended by at least one reputable source1,
and all would heat water long enough to disinfect it and make it safe to drink? Did you also know that it takes one kilogram
(2.2 pounds) of wood fuel to boil one liter (1.06 quarts) of water? The important question then is, in a survival
situation where water and fuel might both be limited, when is boiled, boiled
enough?
In raw water, there are
three kinds of pathogens that are harmful to humans: protozoa, bacteria and
viruses. Common protozoa that are
harmful to humans are cryptosporidium
and giardia intestinalis (also called
giardia lamblia); while commonly,
occurring harmful bacteria are campylobacter,
salmonella, shigella and escherichia coli,
and such common harmful viruses such as enterovirus,
hepatitis A, norovirus, or rotavirus.
Per the CDC (Centers for
Disease Control and Prevention), boiling water is the best method to disinfect
water by destroying dangerous pathogens and making it safe to drink, even when
it is turbid or cloudy, or you are at a high altitude. The CDC states that “Except for boiling, few of the water treatment methods are 100%
effective in removing all pathogens.2” The CDC suggests that prior to boiling,
cloudy water should be filtered through clean clothes, or left to settle,
before drawing off the clear water for boiling.
So what is disinfection,
is it the same thing as sterilization or pasteurization? And what exactly does potable mean? Disinfection means the removal or destruction
of harmful pathogens and is the desired result of water treatment in the field,
where it is typically accomplished by boiling.
Pasteurization, is similar to disinfection, but involves lower temperatures
over a longer time, than disinfection.
The goal of both disinfection and pasteurization is to create potable
water, which means that the water has a minimal microbial hazard. Sterilization is the destruction or removal
of all life forms and is required for surgical purposes.3
In the past and still
today, experts taught and still teach, that water should brought to a rolling
boil for either three to five minutes, ten minutes and some even longer boiling
times. However, research by Howard D.
Backer, MD in 1996, the CDC in 2009 and the World Health Organization (WHO) in
2011; have shown that this is not necessary.
Their research has shown that pathogens are killed rapidly by water
hotter than 140o F (60o C). In fact, their research shows that the time
it takes to heat water on a stove or over a fire, from 131o F (55o
C) to a rolling boil of 212° F (100° C) at sea level will kill all disease
causing bacteria, viruses and protozoa, and therefore disinfect the water. Because of the difference between the higher
standard for sterilizing water for surgical purposes and making water potable
by disinfection or pasteurization, both the CDC and the WHO, now agree that
boiling water for drinking purposes for ten minutes is unnecessary; and in fact,
it is a waste of time, fuel and water.
The Backpacker’s Field
Manual by Rick Curtis stated that water temperatures above
160° F (70° C) will kill all disease-causing organism within 30 minutes and at
temperatures above 185° F (85° C), pathogens will die in few minutes4.
The REI store, in their online camping
skills web site, notes that the most heat-resistant pathogen is the Hepatitis A virus and it is believed Hepatitis A will be killed in less than
1 minute when water is heated to 208°F (98°C)5. In addition, according to the CDC6,
heating water to rolling boil water for one minute has “high effectiveness in killing” protozoa such as Cryptosporidium, Giardia intestinalis (also called Giardia lamblia), bacteria like Campylobacter,
Salmonella, Shigella and E. coli, and
viruses such as enterovirus, hepatitis A, norovirus, or rotavirus.
While most pathogens in
water are killed at temperatures well below the boiling point of water, a
rolling boil is the only easily recognizable visual clue to the temperature of
water without using a thermometer. For
an example of a rolling boil, see the video above.
To be on the safe side, because
of the heat resistance of the Hepatitis A
virus, the CDC recommends heating water to a rolling boil for one minute, and
for an additional three minutes at elevations above 2,000 meters (6,562 feet),
to insure that the water has remained hot enough, for long enough, to destroy
any dangerous pathogens. Similarly, the
National Wilderness Conference advocates bringing water to a rolling boil for
one minute at sea level and boiling it for an additional one minute for every
1,000 feet (305 meters) above sea level, to ensure that dangerous pathogens are
destroyed.
The CDC recommends the
additional three minutes of boiling time because, at sea level the boiling
point of water is 212o F (100o C), however, as elevation
increases, atmospheric pressure decreases and water boils at lower
temperatures. For every 500-foot (153
meter) increase in elevation, the boiling point of water decreases by just
under 1o F or approximately .5o C. For this reason, the CDC recommends boiling
water to a rolling boil for an additional three minutes at altitudes greater
than 2,000 meters (6,562 feet). It will
be noticed, that the National Wilderness Conference is more cautious than the
CDC, as it advocates bringing water to a rolling boil for an additional minute
for each 1,000-foot (305 meters) increase in elevation above sea level. These additional minutes of rolling boiling
time at higher altitudes are intended to ensure that even at these higher
elevations, enough boiling time is achieved to ensure the destruction of any
pathogenic organisms in the water.
Water cannot become any
hotter than 212°F (100°C) and remain in a liquid state. To continue to heat water once it has reached
the boiling point, in excess of one minute at low elevations and an additional three
to six minutes at elevations above 2,000 meters (6,562 feet), merely wastes
fuel, water and time; all of which might be in short supply in a survival
situation. So boil your water only as
long as the CDC recommends or if you prefer to be extra cautious, use the
National Wilderness Conference’s recommendation, and then your water will be
boiled enough.
Notes
1 Choice
a) is the recommendation from the CDC, 2007.
Choice b) is both an old rule,
first recommended in The Survival Book, 1959 where they recommended that
you boil water at a rolling boil for 2 minutes at sea level, later in Survival
FM 21-76, 1986; and it is currently the recommendation from the National
Wilderness Medical Conference (from a personal correspondence with Joe Alton,
MD, August 2018). Choice c) this is a
recommendation from a number of sources, from Survival: Land, Sea, Jungle,
Artic, 1944, which recommended boiling water for 3 minutes; to How To
Stay Alive In The Woods, 1956, and Down but not Out, 1970, both of
which recommended boiling water from 3 to 5 minutes. Choice d) is the recommendation of the
University of Alaska, “Remote Travel Safety Guide”, 2003.
2
“A Guide To Drinking Water Treatment and Sanitation for Backcountry &
Travel Use”, CDC
3 Sterilization
for surgical purposes requires that the water and the items to be sterilized,
be brought to a rolling boil for 15 to 20 minutes [Sharon Greene-Golden, Dr. M.
Baskaran Selvapathy, August Eduard Martin].
4 The
Backpacker’s Field Manual, Rick Curtis
5 Water
Treatment for International Travel, T. D. Wood,
6 A
Guide to Drinking Water Treatment and Sanitation for Backcountry & Travel
Use, CDC
Sources
Angier, Bradford; How
To Stay Alive In The Woods, [Collier Books, New York, NY; 1956] p. 91
Backer,
Howard D.; “Effect of Heat on the Sterilization of Artificially Contaminated
Water”, [Journal of Travel Medicine; 1996] p. 3:1-4 https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1708-8305.1996.tb00686.x, Accessed 4/18/2018
Backer,
Howard D.; “Field Water Disinfection”, https://aneskey.com/field-water-disinfection/, Accessed 4/23/19
CDC, “A Guide to Drinking
Water Treatment and Sanitation for Backcountry & Travel Use”, [2009] http://www.cdc.gov/healthywater/drinking/travel/backcountry_water_treatment.html,
Accessed August 31, 2015
Curtis, Rick; The
Backpacker’s Field Manual, http://www.princeton.edu/~oa/manual/water.shtml,
Accessed August 31, 2015
Green-Golden, Sharon;
“Boiling: The Answer to High-level Disinfecting of Surgical Instrumentation in
a Village of a Third World Country”, [2009] https://www.iahcsmm.org/images/News/Fellow_Papers/FellowshipPaper_SharonGrGolden__2009.pdf,
Accessed May 3, 2019
Martin, August Eduard; Pathology
And Treatment Of Diseases Of Women, [Rebman Company, New York, NY; 1912],
p. 41 https://books.google.com/books?id=xxR50f7ST7wC&printsec=frontcover&dq=%22Pathology+and+treatment+of+diseases+of+women%22&hl=en&sa=X&ved=0ahUKEwjjgZfOioDiAhUiUt8KHV1jCaYQ6AEIKjAA#v=onepage&q=%22Pathology%20and%20treatment%20of%20diseases%20of%20women%22&f=false,
Accessed May 3, 2019
Nesbitt, Paul H., Pond,
Alonzo W. & Allen, William H.; The Survival Book, [D. Van Nostrand Company
Inc., Princeton, NJ; 1959] p. 172
RCAF Survival Training
School Staff, Down but not Out: CFP 217, [Maracle Press Ltd., Ottawa;
1970] p. 121
Selvapathy, Dr. M. Baskaran;
“Sterilization”, [S.R.M.Medical College Hospital] http://www.srmuniv.ac.in/sites/default/files/files/STERILIZATION.pdf,
Accessed May 3, 2019
Survival: Land, Sea,
Jungle, Artic, [The Infantry Journal, Washington D.C.;
1944] p. 24
Survival FM 21-76,
[Headquarters Department Of The Army, Washington D.C. 1986] p. 5-13
University of Alaska Risk
Management Team, “Remote Travel Safety Guide” [University of Alaska, Fairbanks,
Alaska; 2003] p. 7 https://www.alaska.edu/risksafety/download/RemoteTravelSafetyGuide.pdf,
Accessed 4/23/19
WHO, “Technical Brief,
Boil Water, WHO/FWC/WSH/15.02”, [2011] http://www.who.int//water_sanitation_health/publications/2011/dwq_guidelines/en/,
Accessed August 31, 2015
Wood, T. D.; “Water
Treatment for International Travel”, http://www.rei.com/learn/expert-advice/water-treatment-international.html#Boiling,
Accessed September 30, 2015
No comments:
Post a Comment