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If it snows, is it safe to drink the water when it melts? What sickness can I get from snow? I am in Europe and would like to know for here, but other places would be interesting too.

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Are we talking about a backcountry area, or a populated one? Mountaineers routinely melt snow for drinking water. – Ben Crowell Jan 7 at 15:14
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In this situation, as in many others, I would recommend listening to what Frank Zappa has to say: youtube.com/watch?v=TLIppgE45wM – jcdude Jan 7 at 17:16
    
@BenCrowell how far "out of the door" does "The Great Outdoors" begin? – Mindwin Jan 7 at 18:08
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I do not think this is a duplicate, as it ask about general risks, while the referenced question is specific for hypothermia. – imsodin Jan 7 at 19:43
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Day #1, Rule #1 for mountaineering students. 'Don't eat the yellow snow.' – mattnz Jan 8 at 8:36
up vote 19 down vote accepted

If it is clean, fresh snow, it is safe to drink. This is basically drinking rain water. It hasn't had time to pick up pollutants when it is newly fallen. I live in New England, and kids do this all the time. You get taught early to only do this with white snow.

Make sure that the snow is actually clean: the longer it sits, and the more urbanized an area is, the more likely it is to be dirty and to have picked up pollutants. If it's brown or gray snow beside a road or path, or yellow snow where an animal urinated, it's no longer drinkable.

As far as what sickness you can get, it will depend on what's in the snow. With yellow snow, I'd assume you could get the diseases you'd usually get from drinking water with animal waste. If it's beside a road, you'd be ingesting heavy metals and chemicals found in car exhaust.

Edit: In response to the comments as to the general safety of drinking rainwater,

http://www.harvesth2o.com/rainwater_safe.shtml#.Vo7e0pXluAY - This is from a person who tested their own cistern (a holder for rainwater), and includes no information on the cistern's cleanliness, or whether it is open to the air and debris. Even so, the water was purer than well water or tap water the tester checked in New Mexico. The only significant pollutant was bacteria, which tend to grow when you store water.

http://www.who.int/water_sanitation_health/gdwqrevision/rainwater.pdf - In the first sentence WHO simply assumes rainwater is drinkable straight from the sky, and the rest of the article is about storing and purifying after storage. If contamination directly from the sky was a major concern, it is reasonable to expect WHO to mention it when discussing rainwater harvesting.

And anecdotally, when I've lived places where drinking rainwater was the norm, the only concern was bacteria from the cistern, not airborn pollutants.

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Acid rain does not make it dangerous for human consumption @gerrit . It just means it's slightly more acidic than normal. It only causes problems over a long time/in large quantities (i.e. it makes soil more acidic over a long period or time, etc.). "Acid rain" is perfectly safe to drink. In fact there's a fair chance you've drank acidic water today. – Liam Jan 7 at 16:04
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@gerrit, Liam covers why acid rain isn't an issue, but my personal rule (no scientific basis) is that if I'm in a highly industrial area or a city, I won't eat snow that's more than a day or two old because pollutants can settle out of the air. And this is a really conservative rule. But newly fallen snow is as safe as catching rainwater in a glass. – Karen Jan 7 at 18:36
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"It hasn't had time to pick up pollutants when it is newly fallen." I thought rain and snow both picked up air pollutants as they fell. Are you indicating that snowfall is free from pollution as long as it is fresh? – Adam Davis Jan 7 at 20:39
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@AdamDavis I've never lived anywhere that was a concern. Rain isn't 100% pure H20, but neither is tap water. If you are wondering specifically about the purity of rainwater, that should be posted as a different question. – Karen Jan 7 at 21:11
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@Karen I thought this was a question about rainwater safety, which is more precisely a question about purity. I see that you believe there is a distinction to be made between purity and safety. Do you have a reference or a citation to a source that shows that rainwater and fresh snowfall are pure enough to be considered safe drinking water? – Adam Davis Jan 7 at 21:33

From a water purity point of view the same rules apply for drinking water. What is important though is the temperature. If you drink large amounts of snow at a low temperature (i.e. you don't heat it adequately and just drink it as it melts in your hand) then you may need to be careful.

Basically if the temperature is low enough and you're ingesting large quantities of really cold material, it may be enough to tip your metabolism into hypothermia. Typically you should melt the snow (using a stove or fire) before drinking.


Related posts:

Is it safe to put snow in water filtration?

Does eating snow help dehydration?

Do you need to purify all mountain water sources

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The first and accepted answer in your second referenced questions shows that the energy needed to melt snow is not that significant. So getting hypothermia from ingesting snow will be really hard. Before that happens you will simply be unable to get more snow into you from bad stomach and mouth freezing (maybe even frostbite in the face :D ). Funny, at the moment everything revolves around how water cools you :P – imsodin Jan 7 at 15:31
    
Your right @imsodin , what I'm highlighting is it does to certain extent depend on your circumstances. I'm not saying never drink snow. I'm saying if the conditions are right then this could be dangerous. – Liam Jan 7 at 16:02
    
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I joined this community just to upvote your answer. People forget about the hypothermia which can occur. – Martijn Jan 7 at 20:05
    
Welcome to TGO @Martijn – Liam Jan 8 at 9:19

As already explained in the other questions, the primary concern is possible contamination. For fresh snow and far from civilization this is very easy to identify: White is good: yellow, brown, ... not so :)
Close to roads/industry there might be a non-visible contamination but unlikely to be harmful for occasional consumption (at least in countries with enforces environmental standards). And usually this is not the place where you need to get water from snow.

A widespread argument is, that you should not drink demineralized water. Snow is very low in minerals, so this would apply. But is is not true. Minerals can be obtained with the food too. So unless you plan to drink only snow water for days without eating, you are fine. Often a WHO recommendation for adding minerals to demineralized drinking water is quoted as proof for this claim. Apparently this recommendation is to prohibit water contamination from corroded parts of the water conduit system, as demineralized water is quite corrosive.

Another argument is that it will cool you down. This is most certainly true for the mouth, the oesophagus and the stomach, which will be unpleasant and if this is badly ignored, can even cause frostbite in your face...
Russell Steen calculated the energy needed to heat 1 liter of water to body temperature as 67 dietary calories (@ab2 and wikipedia with some calculation suggest 80kCal for melting and kCal for heating, in total 117kCal - does not change the argument though). We ingest and "burn" about 2000 calories a day, so quite a bit more. So you needed to eat more than 1 liter of water worth of snow an our to match this. Of course this is no measure for whether it cools you or not, but it shows the proportions. So unless you are already almost in hypothermia this does not need to concern you too much (the coldness in your mouth and stomach will bother you first anyway).

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65 kilocalories is low. It takes 80 gram calories to melt one gram of ice, if the ice is at zero degrees C. It takes 37 gram calories to raise the temperature of one gram of water from zero degrees C to body temperature. So that would be 117 kilocalories per liter. (Steen is also assuming ice.) But even so, this isn't enough to produce hypothermia unless you are nearly there already. – ab2 Jan 7 at 21:45
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@ab2 Thanks, I added a self calculated version, I don't know what the difference to Steen comes from but I wont look into it - aren't SI, CGS or natural units, so I refuse to look at them any further :) – imsodin Jan 7 at 22:02

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