Boiling Water - How long?

There is fairly universal agreement that boiling water is the best way to rid it of pathogens, but the recommended boiling times vary widely:

"Simply bring the water to a rolling boil and maintain the boil for one minute, regardless of elevation." [/i]Mountaineering; The Freedom of the Hills[i] 8th edition, p. 65

"for safety, you should always boil water furiously for at least five minutes. Increase the boiling time at higher altitudes..."[/i]Outdoor Survival handbook[i] Raymond Mears, p 55

My favorite: "CDC and the EPA recommend boiling water for a full minute (three minutes above 6500 feet... because water boils at a lower temperature.... [/b]However simply bringing water to a boil is just as effective[b]" (emphasis added). [/i]Medicine for Mountaineering[i] James Wilkerson, 6th edition.

I read recently on one internet source, which for various reasons I did not consider reliable, that one should boil water for five minutes, increasing by one minute for each 1,000 foot increase in elevation. That would mean fifteen minutes of boiling at 10,000 feet. If there is any water left in your pot it certainly should be sterile....

Wilkerson makes the point that milk is pasteurized by bringing it to 160F for 15 to 20 minutes. Just in case you were wondering, water boils at 165 degrees on the summit of Everest, so boiling works just about everywhere....

These days I bring water to a boil and then make either coffee, tea, or oatmeal (maybe FD meals), but I wonder if anyone knows of any definitive studies or experiences with boiling water.

I have, in the past, often imbibed from mountain sources without any treatment whatsoever, but mostly that was some time ago, when trails were less traveled. I generally treat water one way or another these days.

This is a general "Water treatment for International Travellers" article. Though it does detail temperature/time of various bacteria and viruses, and has references to sources.


https://academic.oup.com/cid/article/34/3/355/388050#

Hmmm, I carry one of those pocket thermometer thingies (to use a technical term) that is used so I don’t have to guess how hot or cold water happens to be. Does anyone know the temps required to kill the various bacteria, virus’s or other pathogens? If you know the temperature that kills them, you don’t have to be concerned about elevation lowering the boiling temp of water, or extending the time so long there’s no water left in the container.

Actually, Ren's link has charts with temperature and duration. I can't claim to be an expert, but this looks like credible info to me.

Personally, any "extra" boiling after the 1-minute mark depends on the water source.

For a glacier-fed mountain creek, achieving a full rolling boil is plenty -- I don't waste fuel.

On the other hand, if the source is the Amazon or equivalent, I'll boil the devil out of it if I can spare the fuel. I seem to recall that there are lots of spore-stage nasties in tropical water that are tough to kill.

Same goes for a water source with cattle in the area. Cattle are notorious for walking knee-deep into a water source, drinking on one end and simultaneously dropping cow-patties from the other -- ground zero for a huge e-coli load. Boil, baby, boil -- with some campfire charcoal if possible.

On a trip in Western China the locals cooked every food and drank tea made with water just brought to a boil. Much of the water came from cisterns that had livestock wandering about over the ground surface so sheep, pig and yak dung was everywhere. They reported that no one got sick from it. I didn't either. In fact I had trouble in the city from bottled water before I got to the highlands.

If the water is clear, I just bring it to a boil. Otherwise I filter or floc, then boil or treat with chemicals.

Washing hands is more important in my estimation.

Thanks, Ren’s post beat mine by 3 minutes, I was probably typing as he was posting. Good info at his link’s article.

Some years ago, I was in China on a caving expedition. I was the archaeologist and the EMT for the group. Naturally I expected a lot of cases of "Mao's Revenge". There were twelve of us, in country for a month, eating and drinking the local fare.

Not so much as an upset stomach. I am not sure what we consumed, because the wiser course was to just shut up and chew. I was told that our water was boiled regularly....

from the article posted by Ren:

"Because the time required to heat water from a temperature of 55°C to a boil works toward disinfection, any water that is brought to a boil should be adequately disinfected. Boiling water for 1 min or keeping water covered and then allowing it to cool slowly after boiling can add an extra margin of safety [37]. The boiling point decreases with increasing altitude, but this is not significant when compared with the time required to achieve thermal death at these temperatures."

Short boiling times, especially when slow cooling is employed, would seem to be adequate.

Thanks a bunch for this very thorough discussion!

Personally once it's at a boil I'm done. It doesn't need to boil for more than a few seconds. One minute at a boil is overkill.

I have seen all of those methods taught. From my understanding of biology, bringing water to a boil is sufficient for most killing most pathogens. The process of heating it up to boiling, and then cooling it down, exposes the biological pathogen to high enough temperatures for long enough. If you want to be sure, do it longer, if you have the fuel. If you strain all of the suspended solids out, it will improve the effectiveness (of all purification methods).

"if you have the fuel" is the fundamental problem. Keeping the boil going for longer will increase fuel consumption considerably.

BTW, I was off in the boiling time recommended by my questionable source. They advocate ten minutes of boiling plus a minute for every 1000 foot increase in altitude. That's twenty minutes if you are at 10,000 feet!!!

Seems like slow cooling is a really good idea.

I used to work at a hospital and a Dr told me that once water reached body temp the pathogens "thought" they were in you.
at that point they released the DNA,or something like that,which
did the damage.with no body to work on the pathogens unraveled into harmless chemical stew.

From the CDC:
https://wwwnc.cdc.gov/travel/yellowbook/...n-for-travelers

Up here, I only bring to a rolling boil for a minute. Never had problems. Of course, in Canada we don’t have a lot of the nasty things in our water as you would find elsewhere.

I’ve been parts of the world where we filtered the water thru a micro pure pump filter and THEN boiled it for good measure (for several minutes)

After all that we were still nervous about drinking it.

During outdoor activities at home however, My pump filter is one of my favourite and most used bits of gear. I only boil water not if I’m cooking or want something hot to drink. Saves time and fuel.