Water Disinfection: When is boiled, boiled enough…? ©

 

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 140^o F (60^o C).  In fact, their research shows that the time it takes to heat water on a stove or over a fire, from 131^o F (55^o 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. 

 

 An example of a rolling boil.  Video by the Author

 

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.

 

Table 1    Pasteurization Temperature and time

Temperature           Time Required to Achieve Pasteurization

                                                                         (seconds)

162^o F or 72^o C                                                    15.0

192^o F or 89^o C                                                    1.0

194^o F or 90^o C                                                    0.5

201^o F or 94^o C                                                    0.1

205^o F or 96^o C                                                    0.05

212^o F or 100^o C                                                  0.01

Adapted from: “Effect of Heat on the Sterilization of Artificially Contaminated Water”, Table 1, Pasteurization of Grade A Milk, by Howard D Backer

 

The CDC recommends the additional three minutes of boiling time because, at sea level the boiling point of water is 212^o F (100^o 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 1^o F or approximately .5^o 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. 

 

Table 2    Effect of elevation on the boiling point of water       

Elevation feet                                               Boiling Point

Sea level                                                          212^o F or 100^oC

2,000 feet        (610 meters)                            208^o F or 98^oC

5,000 feet        (1,524 meters)                         203^o F or 95^o C

7,500 feet        (2,286 meters)                         198^o F or 92^o C

10,000 feet (3,048 meters)                              194^o F or 90^o C

14,000 feet (4,267 meters)                              187^o F or 86^o C

19,000 feet (5,791 meters)                              178^o F or 81^o C

29,035 feet (8,850 meters) Everest Summit   162^o F or 72^o C

 

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