Melting Snow and Ice for Drinking Water

Drinking-water in Winter

Finding, Collecting and Treating Water

• Fast-flowing streams, rivers and waterfalls are the last places that water freezes, so these should be sought out where practical.
• It is often necessary to break through a layer of ice on a frozen river or lake. In very cold environments, this can be very difficult and often requires specialist equipment such as an ice saw or ice auger, as used in the sport of ice fishing. In less cold environments, the layer of ice is often much thinner, and specialist tools are not required. However, some points of caution are:
  • Don't stand on the frozen lake or river. Keep to the edge of the lake or the bank of the river. If the ice is thin enough to get through without a specialist tool, then it is best to assume it is too thin to safely take your weight.
  • The force required to break through thin ice can still be quite considerable, so it is best not to use equipment such as trekking poles for this purpose, just in case they get damaged. A long ice axe (i.e. a walker's ice axe, rather than a technical climbing axe) is usually the ideal tool. If you don't have one, then a heavy rock with a sharpish point is a good alternative. Drop the rock onto the ice, rather than keeping hold if it, in order to reduce the chance of a nasty accident.
• When collecting ice-cold water, avoid getting your hands in contact with it. For example, tie some cord round the neck of your water bottle (if the design allows it), and dunk the bottle under the water with a stick.
• Water filters are unsuitable for use in freezing temperatures. Once a filter is used, it is impossible to get all the water out of it. Any water inside it will then freeze, i.e. turn into ice and expand. This will destroy the filter material. Worryingly, the filter may still appear to work once the ice inside has thawed, but the water will no longer be filtered properly. In theory, you might get away with a water filter if you kept it always next to your body so that it could never freeze, but in practice it is simply not worth the risk.
• If using chemical purifiers (chlorine/iodine), it is normally better to take chlorine along in cold temperatures, as this remains more effective at lower temperatures than iodine. It is also often recommended to increase the dose of purifiers when the water is very cold, and it is safer to use too much chlorine than it is to use too much iodine. To be safe, for cold water, it is best to double the normal dosage, AND double the normal waiting time that the manufacturer recommends. Also, if possible, warm the water up by keeping it close to you for a while, before drinking it.
• Boiling is regarded as the best way to kill bacteria and viruses in water. In cold temperatures, since there are issues with chemical purifiers as mentioned in the previous point, the advantage of boiling water becomes even more relevant. If boiling water, it is normally recommended to bring the water to a full, rolling boil, and keep it there for about five minutes. The extended boiling time becomes more important at higher altitudes, because water boils at a lower temperature at higher altitudes.

Melting Snow and Ice for Drinking Water

Which is Best: Snow or Ice?

1. Ice. Unlike snow, the volume of ice needed to make water is not much greater than the volume of water you require. Ice also conducts heat much better than snow, due to its structure. It is therefore preferable to melt ice rather than snow.
2. Wet snow. Snow which has a "slushy" consistency has already started to melt. This is preferable to using dry snow. Even if the snow is solid but looks slushy, there is a good chance that it had started to melt then frozen again - it's structure will be closer to ice, and so it is still preferable to dry snow.
3. Dry snow. Dry, powdery snow is the most difficult type of snow to melt. In practice it takes more heat energy to convert it to water, plus the volume of snow required could easily be 10 times the volume of water you are aiming for, on account of the trapped air and the crystal structure of the snow. I.e. if you want a pan of water, you should expect to use the equivalent of 10 pans of snow.

Collection and Preparation of Snow and Ice

Collecting and Preparing Snow

Collecting and Preparing Ice

How Much Fuel Does it Take to Melt Snow or Ice?

The Science of Melting Ice

A Rule-of-Thumb for Fuel Consumption

• For every litre of un-boiled water you expect to drink, take 2 times the amount of fuel that you would need in order to boil a litre of water during summer.
• For every litre of boiled water (for hot drinks, or just to purify the water) that you expect to drink, take 3 times the amount of fuel that you would need in order to boil a litre of water during summer.

Some Practical Considerations when Melting Snow or Ice

• It makes things easier if you have some water that you can put in the pan to start things off. This helps conduct the heat to the ice particles.
• Start off very slowly, and with small amounts (don't stuff the pan) especially if you are melting snow rather than ice. It is important to melt as much as possible without producing steam. It is also important to allow time for the heat to get properly conducted, especially in the case of snow. If you stuff a pan with snow and bang up the heat, the pan can get very hot but the snow is such a good insulator that the heat isn't getting inside the snow. So start with small amounts, and regulate the heat of the pan carefully, which may require lifting the pan off the stove occasionally. Once there is a decent amount of water in the pan, you can afford to be less cautious and increase the heat.
• While melting snow or ice, try to moderate the heat in order to minimise the amount of steam being produced. Even if you intend to ultimately boil the water, it is less wasteful if you first melt all the snow/ice without producing excessive steam, and then, when you have all the water you want, turn up the heat to boil it.
• It is best not to melt snow or ice in a tent or other confined space, for two primary reasons:
  1. It takes a long time and there is a risk of a dangerous build-up of carbon monoxide from the stove.
  2. The steam that is generated will quickly condense and cause problems with wet gear or even ice forming inside the tent.
• The snow or ice is likely to contain large contaminant particles. Once the meltwater has been obtained, it will usually need straining (before any "usual" purification methods take place). This can be done with a clean sock (free from washing detergents, ideally) or other piece of clean material. Coffee filters are a good thing to take along for this purpose. If you are going to use a chemical purifier e.g. chlorine or iodine, it is particularly important to filter out any large particles first (bacteria and viruses can be shielded from the purifying chemicals by such large particles). If you are going to purify the water by boiling it, then any contaminant organic particles are purely an aesthetic issue, and filtering them out is less important.

Some Other Ways to Obtain Drinking Water from Snow and Ice

Snowball on a Stick

Bag Full of Snow or Ice

Melting Snow or Ice with Body Heat

• [Avoid "eating" ice or snow directly. This can result in internal cold injuries and other complications. Only in a dire emergency should this be considered, and little-and-often is advisable, rather than suddenly filling your mouth and body with a lot of cold matter.]
• Put the snow and/or ice into a water bottle or other container with a watertight seal. If you need to use a plastic bag, you will need to be very careful to avoid leaks which could adversely affect clothes, sleeping bags or rucksack contents. A water bottle is usually the best thing to hand, but unless it has a wide opening, filling it with snow and ice is awkward and can take a long time.
• If the container is to be placed close to your body, e.g. in a sleeping bag or inside a jacket, then, for comfort, it should be wrapped in a material which is moderately good at insulating, e.g. a balaclava. It will reduce the rate of heat flow from your body to the container to a more comfortable level, while still allowing the container to be heated.
• A really good way to heat the container is by placing it at the back of a rucksack (i.e. next to your back) while you are active. Once you get going, you will be generating wasted heat anyway, which will be conducted to the container, and in turn this will even help prevent your back from overheating and getting too sweaty.
• Regardless of the method chosen, don't expect water any time soon. It takes a long, long time. The time it takes is impossible to predict. It depends on how cold the ice/snow was, how much heat you generate, and how directly that heat is applied to the container. If you can produce enough water each day to remain healthy, you are doing very well indeed. In theory, it only takes about 80 Calories (i.e. "food" Calories - really "kilocalories") to convert a litre of ice at 0°C into water at 0°C. In practice, though, it is very hard to do. My personal best is about half a litre overnight.

Storing and Carrying Water in Freezing Temperatures

• Consider taking a vacuum flask to keep water in. Even if you put cold, close-to-freezing water in a flask, the flask helps a lot in preventing it from freezing. However, the warmer the water you put in, the better. It is often impractical to store ALL your drinking water in a flask, but even a 1-litre flask full of water is a nice insurance policy in a bitterly cold environment.
• Keep a water container close to your body, so that your body can keep it warm. This means either put it in your rucksack so that it is as close to your back as possible, or better still, in an inside pocket of your coat.
• If you cannot use your own body warmth to keep water warm, and you don't have a flask, then try to fill the container with warm water, and insulate the container as much as possible, e.g. by wrapping it inside a foam mat or other similar material.
• Whatever containers you store water in, expect the water to start to freeze, i.e. take the following precautions:
  • Store the container upside-down, so that if the water starts to freeze, as the ice forms at the highest point, it won't block the unfrozen water from the container's exit.
  • Leave a bit of space in the container (and compress the container a bit, if possible - so that the "space" is a vacuum rather than air). This will give any expanding ice a bit of play before it ruptures the container. It will also help the water move around when the container is being carried, and this makes it harder for ice to form.
  • Ensure the join between the container and it's top (i.e. the screw threads, in most cases) is completely dry before closing the container. Any water that turns to ice there can make it very hard to remove the top.
• If possible, sleep with water containers in your sleeping bag. This might require wrapping them in material first, to make it less uncomfortable if the water is very cold. It also requires water containers with reliable tops, since it becomes imperative that they do not leak when they are in a sleeping bag.
• If you need to store a large amount of water overnight, e.g. at a long-term camp, then insulation is very important. A foam mat is a good source of insulating material, and so, too, is snow. Burying water containers under snow usually helps a lot in preventing the water from freezing - but it is still important to assume that the water WILL start to freeze, and so take the precautions above e.g. store the container(s) upside-down.

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