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Filtering stream water or fresh water is medically unnecessary (slate.com)
38 points by curtis on Feb 2, 2018 | hide | past | web | favorite | 65 comments

Don't follow his advice: All it takes is a rotting animal carcass or infected human poop near your water source to render water unfit for consumption.

Explosive diarrhea and crippling intestinal craps would be a disaster when your miles away from civilization.

Millions of people in the third world die from infected water sources - my church spends millions to help them setup small water filter factories (and setup the economy around it) and it's estimated that $250 in funding helps save one person.

The article nails the phenomenon on the head -- the "outdoor community" tends towards wealthy and educated -- but then completely whiffs on the obvious deduction. Viz., getting sick from waterborne pathogens carries an opportunity cost that is far higher than the price of a filter. I've had such an illness -- from using a malfunctioning filter in a place where it was really necessary, no less -- and it suuuucks. I'd happily pay $100-200 to not have to deal with that again.

How could you have protected against a malfunctioning filter?

By simply bothering to read the user manual beforehand, in fact.

Multiple filters in series, ideally varying manufacturers?

You mean more manual labour filtering presumably filtered water again?

These filters are rarely electric and typically hand operated and partly chemical. (Electric filters tend to fail when you really need them.) Or just heat and apply UV light to water.

That's exactly what I mean:) The stated problem was getting sick when a filter didn't do its job. The question was how to avoid being infected when a filter (silently) fails. My answer is redundancy. This is more expensive in time, money, and effort, but does mean that a malfunctioning filter doesn't mean you get infected.

Exactly right. If you're plane crashed in the Sierras and your trying to survive until rescue can arrive, I can see you risking it (after all a lack of water will definitely kill you, water with Giadarsis in it will just make you sick). But If you are hiking/camping and you have the opportunity to bring something that can filter out that stuff, you will avoid some seriously nasty bad times.

> Exactly right. If you're plane crashed in the Sierras and your trying to survive until rescue can arrive, I can see you risking it (after all a lack of water will definitely kill you, water with Giadarsis in it will just make you sick). But If you are hiking/camping and you have the opportunity to bring something that can filter out that stuff, you will avoid some seriously nasty bad times.

It's a bit of a trade-off. If you're off camping for a long weekend and your purification system fails but you're in an area with a body of fast moving water, then you might be better off drinking from that source and hoping for the best because symptoms won't hit you until you're back in civilization.

If you're stranded, and you're uncertain when rescue is going to come, then catching a parasite from a dirty water source can drastically reduce your chances of surviving until you're found.

Cramps and diarrhea, meh. The concerns are many though. Osmotic diarrhea from the cholera dead carcass is shedding can kill you in a 48 hours (this was a huge problem for the Kurds after the first gulf war and in Haiti in ... 2012?). Shistosomiasis, tinea solium, etc, etc.

And the risk with the asymptomatic infections is that you become the vector. See Typhoid Mary. Giardia may not kill you, but it might stunt your kid's growth.

Finally, 5.7% risk of infection is non-trivial. If the was a 1:20 adds of you falling and hitting your head in the shower, I bet you'd take baths or just skip bathing entirely.

I second this. In one camp, when I was a boy-scout, we took the habit of drinking in streams. Halfway through the camp, we had a diarrhea epidemic, which made us much more cautious about this.

Amen. I drank from a "clean" mountain stream next to my campsite on a weekend trip, then the next day I noticed there was dead mouse upstream.

Don't know if the dead mouse was the direct cause or not, but after returning home I had Giardia and needed strong drugs to recover, thankfully it wasn't a week-long trip.

I was on a cave tour once and there was a crystal clear spring fed stream running thru the cave. The guide said something like the water looks good to drink but then we went around the bend and there was a giant pile of bat guano sloping down into the water.

Anecdotally, I've had gallons of water from lakes in Northern MN while camping, and it was delicious. On the other hand, also anecdotal, one of my ancestors in Germany is said to have died from infection after drinking from a pond in Germany. More recently, a family friend became seriously ill after drinking from a mountain stream -- they think it may have been due to a dead animal upstream from the location. The rule-of-thumb I was told is to take water from the middle of the lake, and not near or downstream from any streams that might feed into it. I wonder if this article is perhaps understating the risk, or maybe giving people ideas that could lead them to engage in potentially life-threatening behavior, particularly if they are not experienced in back country survival. Yes it is often OK to drink from fresh water sources, but it is not a myth that people get very sick and/or die from it.

Water filtration may be mostly unnecessary, but water purification (elimination of gut-crunching pathogens) is another story. If you're in a true survival situation, taking a chance on drinking water that could have dangerous pathogens is probably not worth the risk. Every water source is different and carries a different risk profile (how far upstream, where the water is sourced, etc).

You don't need to buy anything to purify water. Oddly this article did not discuss the simplest method of all - just boil it. A steel, non-insulated water bottle works fine.

You don't even have to boil it, technically. Most pathogens die at a much lower temperature, given enough time.

For what it is worth, our backwoods trip had us looking for clear, running water that had a small amount of green stuff growing in it, on the theory that if it wasn't killing greenery, then it wasn't killing you. Then, a treatment with off the shelf iodine tablets. No filtering needed. The iodine added an unpleasant taste, but I thought that was better than the gut-crunching alternative.


I've met a backpacking couple who never filter. They fill their water bag from any deep source (lake or river) by swimming out, diving deep and filling the bag there. Because they believe most organisms live in the top few inches. Worked for them; a decade of backpacking all over the world.

On the other hand, one of our Scout leaders got giardia at Boundary Waters, due to incorrect filtration habits. So the article claiming no correlation exists may be an exaggeration.

In Norway, where statistics show about 80%(!) of the population go hiking in the mountains at least once a year, almost nobody uses a filtration device. And we don't all get sick. Official advice is that drinking from streams is fine when you're not downstream from human habitation or livestock grazing areas.

Or these relatively cold streams harbor few parasites evolved to thrive at human body temperatures -- I would not carry this practice to warmer areas of the world.

> On the other hand, one of our Scout leaders got giardia at Boundary Waters, due to incorrect filtration habits. So the article claiming no correlation exists may be an exaggeration.

Am I not well educated on filtration. I did become terribly ill after drinkring unfiltered stream water. Given the outcome, I won’t ever do so again unless I’m hopelessly lost without provisions.

Same here. I get the feeling that whoever wrote the slate article hasn't been where we have. Filtration is worth it for my weak biome.

I have heard it the other way. Supposedly UV will kill germs in the top layer of a lake so you should use that water :)

UV will kill most microbes, which is why things like the UV pens are good for purification. However you need to at least run it through a filter first to remove large particulate matter, as the UV won't penetrate into those and kill the microbes inside. Most filters also won't catch viruses and bacteria, just protocysts and dirt.

The article vastly overstates it's conclusions to dangerous effects. A cursory search of medical literature finds plentiful epidemiological evidence. Cases of water borne sickness are not infrequently reported all over the country. One cannot rely on visual clues alone to confirm absence of human or agricultural activity nearby. Worse yet, backcountry hikers may quickly find themselves in a life-threatening situation even after a mild injury or persistent symptom, like diarrhea. A twisted ankle is no big deal in the city, but a serious medical emergency when you are on top of a mountain.

One does not have to buy the hype of big filter---just boil your water or use iodine to stay safe.

As someone who got Hepatitis A from drinking from a mountain stream in deep Himalayas ( however deep you go in India you always have someone above you shitting in the water), I always carry an Iodine tablet with me now.

Water filtration straws are cheap and easy to use. There is no reason for the risk, especially not while out in the wilderness.

Agreed. Filtration systems are cheap, and even if you don't have one with you it's pretty easy to boil water to be sure.

In the extreme case that you can't boil the water, try collect rain water or water closest to an in-ground source (top of a stream where it comes out of the ground or a natural spring).

The biggest risk factor imo (outside of personal hygiene) is not knowing what lies further upstream. Only takes one dead animal to make you have a real bad time.

Iodine water treatment is even cheaper, more effective against viruses, and you don't have to guess about the age of the filter. I've been using the same bottle of Polar Pure for about a decade.

…most of the time.

"The idea that most wilderness water sources are inherently unsafe is baseless dogma" may be true, but if you only need to hit one sometimes unsafe source at the wrong time to be in trouble.

I’ve been a big outdoors person all my life and regularly go backpacking and drink mountain stream and spring water. I’m also a big advocate of being realistic about risks and not sweating stuff that’s scary but extremely unlikely.

That said, I know people personally who have had giardiasis. It’s awful. On a typical backpacking trip I’ll get water from from a bunch of different sources along the way, often not knowing what’s upstream. A few seconds of stirring my water with a lightweight UV sterilizer pen which I bought for $60 years ago is relatively low cost insurance against a risk which is hard to assess in the moment.

My understanding is that much of the research on giardia et al has been in a few specific wilderness areas, and widespread sampling studies of many water sources are fairly few, so using what little research does exist to inform my decision to drink directly from a random mountain stream seems dubious.

Someone tell Nikolay Przhevalsky that his cause of death was not linked to drinking from a stream: https://en.wikipedia.org/wiki/Nikolay_Przhevalsky

Just need a dead animal a bit upstream and you get a lot of goodies.

a filter wouldn't have helped any, they dont protect against bacteria.

Bacterial removal depends on the size of the filter. Microfilters remove many bacteria, including Campylobacter, Salmonella, Shigella, and E. coli.

Ultrafilters do most bacteria (and many viruses).

See https://www.cdc.gov/healthywater/drinking/home-water-treatme...

Lifestraw, for example, does 99.9999% of bacteria. See http://www.lifestraw.com/faqs/

Typical portable water filters do remove bacteria, but not viruses.

that's why you put iodine tablets in and/or cook water.

Source? The LifeStraw claims to filter out 99.9999% of bacteria, which makes sense, since bacteria are large and thereby easily filtered relative to other contaminants like viruses and dissolved metals.

Someone tell these guys it's cool, they can ditch their straws:


The article specifically states that it concerns areas not trafficked by humans and pack animals.

The people in your linked article would likely still need to take additional precautions.

I'm mainly complaining about the American world view of everyone on the internet being other Americans within the borders of the United States. Take eBay for instance, with the majority of American sellers flat out refusing to ship internationally, even to western Europe.

I get that they don't want to sell me yellowcake, but I don't see the harm in sending me a few obsolete computers from the 1980s.

They refuse because it's a pain in the ass to ship internationally and there are probably plenty of buyers in the US.

Wherein lies the pain of shipping internationally from the US?

Whenever I've shipped stuff, whether through the regular postal system or the big name couriers, they don't seem to care where in the world the recipient is, other than that different places call for different rates, which I suppose is fair. And eBay accounts for this too.

Giardia is carried by bears and beavers, not just humans and pack animals.

It's commonly known as "beaver fever", in fact, and by all accounts it is not a fun experience (2-6 weeks of explosive diarrhea for some).

OTOH, I'm perfectly okay paying REI $40 once every few years to not verify this.

> To be clear, there’s no question that Giardia lamblia, Cryptosporidium parvum, and various strains of fecal coliform bacteria—the waterborne pathogens responsible for giardiasis, cryptosporidiosis, and other diseases—can infect humans, with potentially serious health consequences. Yet research to date has failed to demonstrate any significant link between wilderness water consumption and infection with these threats.

So what vectors are there for those threats, if not unfiltered 'wilderness water'?

I've wandered the Scottish Highlands for many years camping and using bothies never filtered water - mind you I mostly consume coffee or tea so maybe the small amount of boiling killed off any beasties. Mind you - I am fairly careful about where I get the water (check for any dead animals upstream, don't take water from anywhere that is obviously frequented by animals or people).

Meanwhile, my wife got a nasty case of cryptosporidium - GP suspected it was from a swimming pool!

Boiling is what did it. Boiling is the most sure-fire way to disinfect water.

Unless contaminated chemically, e.g. by heavy metals. Most portable filters do not protect against these though.

Most portable filters will, actually. They've got fine enough filters to catch protocysts; they'll easily catch any metal contamination. What they don't get are smaller bacteria and virii, which is where secondary purification in the form of boiling or purification tablets is necessary.

> So what vectors are there for those threats, if not unfiltered 'wilderness water'?

Lack of hygiene in the wild?

> the journal Wilderness & Environmental Medicine, concluding that instead, details “point compellingly to hand-to-mouth transmission.” Put more simply: The afflicted campers failed to properly wash their hands after using the bathroom.

You don't get giardiasis from "failing to wash your hands after using the bathroom". You get it from drinking water contaminated with animal feces.

There is absolutely no doubt about this.

That doesn't even make sense, if you think about it. The only way to be exposed to one of these diseases from your own feces would be if you already had the disease.

Washing your hands can help prevent infections from spreading to others, certainly, but your own gut microflora is extremely unlikely to pose a threat to you personall.

Hand-to-mouth can be from touching things in the environment contaminsted with animal feces without washing properly before, e.g., eating. It doesn't have to be your own feces.

The food industry maybe?

Anecdotally evidence: I've been backpacking for 25 plus years and am an avid filter user. But I have met dozens of people who do not, almost all on the AT (where I backpack the most). In the 90's it was quite common to find thru-hikers not using a filter. I have never met anyone who got sick from unfiltered water.

Will this change my behavior. Probably not. But I will stop treating my contaminated side of the filter like it it covered with ebola.

You should avoid that contamination. The raw water does contain bacteria, just in low enough doses for your immune system to handle it. You have deliberately concentrated days worth of bugs in a small spot, so it’s likely to be nasty.

Would UV light help mitigate that small spot's infectiousness?

After reading this thread, I'm writing to MSR about whether treating their Guardian filter with my ozone generator in a small box to 1 ppm for half an hour after I get back would void their support. I don't touch it now, but I'd rather kill the bugs than leaving them to desiccate in storage.

What does the phrase 'medically unnecessary' really even mean? Does it mean 'not necessary to filter your water except in those cases where it is necessary to filter your water'?

I think the article is saying the risk of a problem is low, so it's not necessary to filter. That's a silly statement to me and seems totally subjective, not objective. I'll decide how averse I am to risk, given the costs involved.

1 in 20 is not low odds at all. Ask any D&D player.

Are you sincerely arguing that a 5% chance of something happening is not a low chance? Either way I don't really feel like arguing about relative chance.

If I see it come out of the ground I have zero issues drinking unfiltered water. With a filter I prefer streams first, lakes second, and ponds last in terms of preference. I have made exceptions at high altitude and drunk from streams without a filter, but the idea of crippling diarrhea 20 miles from anything is frightening, and boiling water isn't always convenient on long trail days.

Most of the time, Russian Roulette is perfectly safe. But sometimes it's very dangerous.

There's a rebuttal that was posted a few days after this, here's the HN link: https://news.ycombinator.com/item?id=16320964

So I'm addicted to the flavor of iodine tablets for nothing?

The recommendation for survival situations is to purify, treat, or boil your water if you possibly can. If you can't, then you should consider drinking water without processing, the theory being that it's better to get sick with something that probably won't kill you in 3 days rather than die of dehydration in the next 12 hours. The calculus changes quite a bit if the unprocessed water likely won't even make you sick.

Depends on the situation. Generally in temperate climate you wouldn't dies off dehydration in 12h of even quite strenuous work. A day is typically survivable and you would have quite a range to reach something potable or appropriate hardware.

Now, if you went on a trip in sunny climate, you're in luck as UV can be used to disinfect most containers. Does not take too long.

In very cold climates frozen rainfall (snow, ice) is an excellent source of water if you can melt it.

The highest risk is tropics, as high temperature, humidity and lack of sunlight make obtaining potable water or purifying it difficult, so unless you know which watery plants to eat you might be in serious trouble.

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