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I know that the antifreeze used in fresh water RV tanks is non-toxic and can protect to -50F.

Thinking Sugar might be a good choice I posted the question How to calculate how much sugar to use as antifreeze in drinking water? from the answer it looks like you don't get much real benefit for reasonable amounts of sugar.

So what potable/drinkable additive can I use to keep my drinking water from freezing? How much of it do I need to use to get to protect at different temperatures.

Optimally the answer includes a chart that shows the volume to add per unit of water, for an anticipated temperature.

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    Or you could do the experiment with cheap wine and your freezer.
    – ab2
    Commented Jan 19, 2016 at 2:17
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    @ab2 alcohol and cold temperatures have negative issues when used together on the human body.
    – James Jenkins
    Commented Jan 19, 2016 at 11:23
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    Remember to store your bottle upside down. That way when ice floats upwards and freezes you can still drink out of the bottle.
    – QuentinUK
    Commented Jan 20, 2016 at 17:29
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    @QuentinUK the ice tends to form on the side (that is where the cold is) it will also sometimes create a lattice that holds it in place. If the bottle is not moving around I don't think you will actually have any added value based on how it is stored.
    – James Jenkins
    Commented Jan 20, 2016 at 17:36
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    Whatever you do, just remember that you need to be careful that it does not damage you just by drinking it so cold. Even if I could drink water that was 30 degrees below freezing temperature, I might not want to, and I might want to heat it up closer to 0C/32F anyway just to make it safer. I'm not sure if it's a universal term or not, but we call it "brain freeze" when you ingest something too cold, and it can be very painful, and it affects more than just your head, despite the name; it can cause problems in your upper head, eyes, neck, stomach, possibly more. It gets me bad in the neck.
    – Loduwijk
    Commented Apr 28, 2017 at 16:37

5 Answers 5

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There are two natural options; none of them is quite pleasant.

Alcohol

Per Wikipedia, 8.5 vol% of ethanol make the freezing point drop to -3C (26.6F) (more values at at Wikipedia, also a diagram is available below).

enter image description here

Most of the ethanol will be evaporized during cooking, so it's not that much an issue; also 14 vol% is only 6.8 wt%, so the added weight is 6.8%, which sounds like a lot, but still it's 1/15 only. The good thing is that you can get cheap and quite strong alcohol almost anywhere around the world. Of course, this has some issues, such as where to get spare alcohol for a longer journey; also, some alcohol will be always left in the solution, no matter how hard you try, which is not good at winter.

Note that you can get a 90% alcohol at special shops, but it can get quite expensive because of the excise tax. Don't buy technical alcohol, it's denaturated, i.e. very disguisting and possibly not really safe to drink.

Salts

Note that you can't really do much with salts. The most efficient salt is NaF (sodium fluoride). However, it is poisonous, lethal dose is around 8g/100kg weight. We can compute that even a huge amount such as 34 grams of NaF in 1 litre of water reduce the freezing point to -3C. However, that's 3.4 wt%, which is freakingly lot.

For NaCl (kitchen salt), the amount to get to -3C is 47 grams, so almost 5%. Since the relationship is linear, any reasonable amount of salt has close to zero effect on the freezing point.

Conclusions

Do not do this. Find other methods how to supply yourself drinking water in extreme conditions.

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    Please note that if there is nothing obviously wrong with my answer and you do not explain what is wrong with it, I ignore the downvote. Thanks.
    – yo'
    Commented Jan 23, 2016 at 8:39
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    (-1) none of the "options" is actually an option. NaF is even more toxic than ethanol: according to the safety data Wikipedia cites, the lethal dose for humas is about 5 - 10 g. Fortunately, you won't be able to easily obtain NaF to perform the described experiment. NaCl at 5 % is higher than the salinity of the mediterranean sea and undrinkable (besides totally defeating the purpose of drinking water). I don't think we need to discuss the inadvisability of relying on Doppelkorn/vodka or similar schnaps in cold outdoor conditions. Not to speak of the fact that your graph misses an ...
    – cbeleites
    Commented May 3, 2018 at 16:56
  • ... important part of the ethanol/water phase diagram: there should be two lines, solidus and liquidus. (I think the given one is the liquidus). They tell you for a given temperature what the composition of the solid ("ice") and liquid phase are. What happens with the schnaps is that you'll have a water-rich frozen phase and the liquid gets even more concentrated in alcohol. (This is used for producing some types of strong beers: Eisbock / Ice Rifing)
    – cbeleites
    Commented May 3, 2018 at 17:13
  • Have you got a source that ethanol evaporates fast (as in a large part will be gone by bringing water to boiling point and keeping it there for a minute or two) when boiling water wiyh ethanol in it?
    – Bent
    Commented May 4, 2018 at 10:43
  • @cbeleites Thanks for the note about NaF being poisonous, however, my whole point is about salts not really helping.
    – yo'
    Commented May 6, 2018 at 14:12
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It's pretty easy to keep your water from freezing without adding anything to it, actually. If you keep it under your shell, your body heat will keep it from freezing. If you bury it under a foot or so of snow, it will stay liquid overnight (although you may get a little ice around the edges). If you boil it and put your hot water bottle in your sleeping bag, it won't freeze and you'll have toasty-warm feet. Insulated bottle jackets and vacuum-sealed thermoses are also awesome.

And if you need water in larger amounts, just melt snow or ice (haul a block with you, if you won't have snow), or bring an ice axe to get through the ice covering a nearby body of water. (A small hole is all you need; the water pressure will fill the "bowl" you chipped away to get down to the bottom of the ice.)

There may be chemicals that will get the job done, but it seems to me you will almost always be better off with good old water.

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    While I agree, this answer does not address the very specific question put forward by the OP.
    – ShemSeger
    Commented Jan 18, 2016 at 22:27
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    A good thermos with hot water in the sleeping bag is no use, though ;-)
    – gerrit
    Commented Jan 19, 2016 at 16:11
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Propylene glycol is allowed in alcoholic beverages up to 5%, and this would get you to about 29°F.

You could probably throw in a little sugar, salt and good old ethanol to kick it down further. Really, nearly any solute will push down the freezing point. Maybe some salty chicken bullion, plus alcohol just to keep it from rotting. This is starting to sound like a bad idea.

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If you need a water supply that will not freeze without additives, dig a hole in the ground. In the hole place a hard sided cooler . The top of the cooler should be no less than 1 foot below ground level. Drape a small tarp or other heavy material that will not degrade. The tarp will rest over the cooler and overlap the sides of the hole. Fill over the top with clean backfill. Place a wooden rod on 2 opposing sides of the tarp that come out of the hole and staple the tarp around the rod on each end to be used as handles. Whenever you need access place your foot on one handled side and pull the other side up, dirt and all. Get your drink, and put the tarp and dirt back in place. This works and is a common sense approach to having good old drinking water that will not freeze and has worked for me in winter camps where temps dove to 15 F at night. Hope you find this fairly simple approach useful.

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  • I failed to mention in the above comment that RV water line antifreeze (for potable lines) should never be used to lower the freezing point of water to be consumed. Full flushing of the lines is recommended. It will taste terrible and consumption is not intended. It is non-toxic but was never meant for consumption. Read the SDS.
    – Simple Man
    Commented Nov 26, 2019 at 20:29
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    You can edit your answer, with the edit button under your answer.
    – James Jenkins
    Commented Nov 27, 2019 at 11:07
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Electrolytes

You can use an electrolyte solution in your water. Many do this for obvious other reasons but it will reduce the freezing point in the water.

I'm sure you've seen the various powders at health food or supplement stores.

I wish I had a good citation but sodium (Na+), potassium (K+), calcium (Ca2+), magnesium (Mg2+), chloride (Cl−), hydrogen phosphate (HPO42−), and hydrogen carbonate (HCO3−) all reduce the freezing point of water a bit and if your working hard are essential to body chemistry.

Good for you and reduces the freezing point.

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  • The problem is the reduction depends on the molar amount of the additive, so you only do quite well with substances whose molar mass is low. And then, even NaF with a very low molar mass is necessary in huge amounts to have any significant effect.
    – yo'
    Commented Jan 23, 2016 at 8:41
  • Citation: pretty much any textbook on physical chemistry/thermodynamics will do. And actually you don't need an electrolyte, all dissolved substances do reduce the freezing point. However, what happens is that for many substances, solius and liquidus do not coincide, so you'll typically get watery ice and a highly concentrated rest of solution, so not really an improvement over the "some ice in water" situation (the more so, as the highly concentrated solution are not good against thirst - water is needed there)
    – cbeleites
    Commented May 3, 2018 at 17:22

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