Melting snow for water – how the family gets drinking water in winter

It is dark at four o'clock, and the tent is finally up. Someone asks for water. The flask from home has been empty since lunch. The pot is filled with fluffy snow, the stove is lit, and five minutes later there is a splash of grey water at the bottom. There is a burnt smell. The pot is filled again. And again.

By seven o'clock everyone has had a mug of hot chocolate, the pasta is not cooked and the canister feels suspiciously light.

There is nothing wrong with the stove. The problem is that nobody did the maths. Snow looks like an endless supply of water, but it is mostly air, and melting it costs more fuel and time than almost anything else at a winter camp.

The model to remember: count, choose, melt and save

Water gets easy if you take it in four steps:

1. Count. How many litres does the family need until the next morning, and how much fuel will that take?
2. Choose. Which snow gives the most water and is the cleanest?
3. Melt. How do you get water out of the snow without burning the pot or wasting fuel?
4. Save. How do you keep the water liquid for the evening, the night and the morning?

The bigger picture of sleeping outdoors in the cold is in winter camping: camping and sleeping outdoors in winter. How the stove works in the cold, with winter gas, a spirit stove and a food flask, is covered in cooking outdoors in winter. This page is only about the water.

Count: how much water does the family need?

The crisis figure from Livsmedelsverket, the Swedish food agency, is three to five litres of water per adult per day for drinking, cooking and basic hygiene. It is meant for a crisis at home, but it fits a winter camp surprisingly well. There, all the water for cooking has to come out of the snow too: the pasta water, the porridge, the evening hot chocolate and the flasks for the morning.

According to the Nordic Nutrition Recommendations, an adult needs roughly two to two and a half litres of water a day from food and drink. That applies at normal temperatures and with moderate activity. A day with a pulk and skis is not moderate, and physical activity increases the need.

Count like this: roughly three to four litres of melted snow per person per day. Children need a little less: roughly 1.6 litres a day from food and drink between the ages of four and eight, and around two litres from the age of nine. Still, count the children as adults when you plan. Whatever is left over goes into hot water bottles, the washing-up and an extra mug of hot chocolate.

For a family of four that comes to twelve to sixteen litres. That is a lot of snow and a lot of fuel, which is why it pays to do the maths beforehand.

Where the water goes

Go through the evening and the morning and count the mugs and pots:

• Dinner. Pasta, couscous or porridge needs its water, and it is easy to forget in the count.
• Evening drinks. A mug holds about three decilitres. Four people drinking two mugs each need almost two and a half litres.
• Flasks for the night and the morning. Fill them with boiling water before you go to bed.
• The hot water bottle. It warms a sleeping bag at night and becomes the morning's water, so it only counts once.
• Breakfast. Porridge and a hot drink.
• Bottles for the day. What you will drink during the day until the next camp.

Most of it can be melted in the evening and at breakfast. Melt the day's drinking water while breakfast is cooking, and keep it in a flask.

When there is not enough water

Mild dehydration shows up as a headache, tiredness, dizziness, irritability and a poorer appetite. At a winter camp, it is easy to blame these on the cold, the dark or a long day. Drinking is easily forgotten in winter, when water is a hassle to get and nobody feels thirsty.

A headache in a tent with a stove or a cooker can also be carbon monoxide. Air the tent, get out into the fresh air and read the signs in carbon monoxide in a tent before you decide it was just too little water. If several people in the tent have a headache or feel sick at the same time, everyone must get out immediately.

Count: how much fuel does the snow cost?

This is where most people get their sums wrong. Melting snow costs much more than boiling water, and the reason is physics.

Why snow is so expensive

To turn a litre of snow at minus ten degrees into boiling water, the energy goes to three things:

Step	Energy for one litre
Warming the snow from minus ten to zero degrees	about 21 kilojoules
Melting the ice into water	334 kilojoules
Heating the water from zero to 100 degrees	about 418 kilojoules
Total	about 770 kilojoules

Just melting the ice, in other words, takes as much energy as then heating the water from zero to about 80 degrees. Boiling a litre of tap water at ten degrees takes only just under 380 kilojoules. Snow takes roughly twice as much energy as water from the tap.

From kilojoules to grams of gas

Propane-butane gas contains roughly 46 megajoules per kilo. If all the heat ended up in the pot, a litre of boiling water from snow would take about 17 grams of gas. For a family that needs fourteen litres, that comes to around 240 grams, and that is the absolute minimum.

In reality, much of the heat ends up in the air around the pot, and even more when it is windy. Cold, wind and melting snow can take three to four times as much fuel as boiling water in normal conditions. A wind of eight kilometres an hour, a fairly light breeze, can triple the consumption of a stove with an open burner.

Do a test at home with the kitchen scales

No table can tell you how much your particular stove uses. A test at home can.

1. Weigh the canister on the kitchen scales and write down the weight.
2. Melt a full pot of packed snow out on the balcony or in the garden on a cold evening, with the lid on, until the water boils.
3. Measure the water in a measuring jug and weigh the canister again.
4. Work out grams per litre and multiply by the family's litres for the whole trip.
5. Add a reserve for wind and for anything that gets spilled or burnt on.

The test also shows how long a pot takes, which is good to know when it is dark and the children are hungry. The fuel and the pot then belong in the winter camping packing list.

Tip: Several stoves make melting snow faster. If there are two adults with a stove each, one can melt snow while the other cooks.

The wood stove does the job for free

If you have a tent with a wood stove, it is burning all evening anyway. A pot of snow on the stove melts on wood instead of gas, and in our test of a tent stove heating water on top of the stove worked without any problems. Keep the lid on the pot so the steam does not turn into frost on the tent fabric. How to set up the stove and burn it safely is covered in tents with a stove.

Choose: which snow gives the most water?

Fresh snow is mostly air. Freshly fallen dry snow weighs 30 to 100 kilos per cubic metre, while packed late-winter snow weighs 200 to 300 kilos. A pot of fresh snow therefore gives only a splash of water, while the same pot of packed snow gives several times as much. The table on this page shows how many litres of snow it takes per litre of water.

A three-litre pot filled with packed late-winter snow gives about six to nine decilitres of water. Filled with dry fresh snow, you get one to three decilitres.

How to find the best snow:

• Dig beneath the surface. The loose top layer is the airiest. A little further down, the snow is often packed and heavier.
• Cut from a drift. Wind-packed snow can be cut into blocks with the shovel, and the blocks are easy to carry.
• Pack the snow in a bag. Fill a sturdy bag with snow. The snow gets packed as it is carried, and the bag becomes a store by the stove.
• Ice gives the most. Chunks of ice from a lake are almost pure water, but only take them from ice you know will hold.

Water from a hole in the ice saves the most fuel

Sometimes you can get drinking water from a hole in the ice, if the conditions are right and you have something to make a hole with. That saves a lot, because the water is already liquid. The melting step, just over 40 per cent of the energy, disappears.

Always boil lake water. Only go out on the ice if you know it will hold, and read ice safety with kids before anyone in the family heads out with an auger or an axe.

Choose: is the snow clean?

Snow that has just fallen far from roads and people is usually clean enough to melt. It is the snow around you that becomes the problem.

Bacteria and parasites

Snow close to a camp may contain urine, droppings from dogs and animals and dirt from boots. The cold does not make it clean. Cysts of the giardia parasite survive a long time, especially in cold and damp conditions, and it takes very few to make you ill. So never drink untreated water from lakes and streams.

Bacteria, viruses and parasites die when the water boils with big, rolling bubbles. Let melted snow boil for a while.

This needs to be boiled:

• water to be drunk as it is or mixed with squash
• water for the children's bottles
• all water from a lake or a stream

This does not need to be boiled separately: water that boils in the pasta, the porridge or the soup anyway. That saves a whole round of fuel.

Chemicals and dirt

Boiling kills bacteria and parasites, but it does not make water containing fuel or chemicals safe. Salt and soot stay in the water. Snow in towns picks up pollution from traffic, road salt, grit and fallout from the air. So never take snow from a snowplough bank, a roadside, a car park or a snowmobile track.

The three corners of the camp

Decide where everything goes before anyone has had time to walk on the snow:

1. The snow corner is a little way from the tent, ideally upwind, in untouched snow. Mark it with a pole or a stick and let nobody step there.
2. The kitchen is between the snow corner and the tent, on a board in the snow and out of the wind.
3. The toilet corner is far away in the other direction, downwind.

It sounds obvious, but in the dark with a head torch all snow looks the same. Show the children the corners while it is still light.

Leave any snow with colour, pine needles, soot or animal tracks where it is. If the water tastes odd even though it has been boiled, pour it out and fetch new snow somewhere else.

Melt: fast and without a burnt taste

There are only a few basics, but each step saves fuel or a pot.

1. Always start with water in the bottom. Dry snow against a hot base burns on, and the water tastes burnt. Save a splash of starter water in a flask from the previous round, so the next pot gets going straight away.
2. Add the snow a little at a time. Top up as it melts, and stir. A big mound of snow on top of a small puddle insulates and melts slowly.
3. Put the lid on. It saves fuel, and a big enough pot makes melting faster.
4. Melt a lot at once. Lighting the stove once and melting enough for all the flasks saves more than boiling one mug at a time.
5. Boil what you are going to drink. Let it bubble hard for a while, and pour it into the flasks straight away.

Put the stove out of the wind, but never enclose a gas canister completely. The canister can overheat. This is explained in more detail in the guide to cooking outdoors in winter, along with what to do if someone gets burnt.

Never melt snow in a closed tent

Melting snow takes a long time, and it is tempting to sit in the porch when it is windy. A gas stove or spirit stove in a closed tent can produce carbon monoxide. Melt the snow outside. If the weather forces the stove into the porch, the porch must be fully open, someone must sit awake next to it and the stove must be turned off as soon as the water is ready.

The taste

Melted snow often tastes flat. Meltwater lacks the minerals found in tap water, and squash, a sports drink or a little salt and sugar make it taste better. During physical exertion, the body also needs salt along with the fluid. A mug of stock in the evening gives you both, and children drink more when it tastes of something.

Save: keeping the water from freezing

Saving the water is just as important as melting it. Water that freezes in the bottle has to be melted all over again.

• Flasks of boiling water. Fill them before you go to bed, and there will be water for the morning porridge without anyone having to light the stove in the dark.
• A bottle in the sleeping bag. Fill a bottle with hot water, pull a wool sock over it and put it in the sleeping bag. The bottle must have a tight lid and be able to take the heat. It gives warmth at night and liquid water in the morning. Children should not sleep with the hot water bottle, so it goes in an adult's sleeping bag. How the bottle pre-warms the child's sleeping bag is covered in winter camping with kids.
• The bottle upside down. Ice usually starts to form at the surface of the water. If the bottle stands on its lid, that ice ends up at the bottom of the bottle instead of in the thread, and the lid is easier to unscrew. Check first that the lid is watertight.
• Bury the water container. A water container or bucket buried in a snowdrift keeps the water liquid even when it is quite cold. The snow insulates.
• A small cool bag in the pulk. It keeps the cold out in the same way it keeps the heat out in summer, and ordinary bottles stay liquid for longer.
• Do not fill to the brim. Ice takes up about nine per cent more space than water, so a full bottle that freezes can split.
• Close to the body during the day. A small bottle in an inside pocket does not freeze and is to hand at every break.

More on how the bottle and the sleeping bag make the night warmer is in staying warm in a tent in winter.

The children and the water

Children forget to drink when they are playing, and they rarely say they are thirsty when it is cold.

• Their own mug with their name on it. Every break starts with everyone drinking a mug.
• Lukewarm, not hot. A warm drink is lovely, but top it up with cold water so nobody gets burnt.
• Something sweet when someone is cold. A shivering child needs something sweet to drink and dry clothes. What to do if that does not help is in hypothermia and frostbite.
• Give the child a job. Digging packed snow for the snow corner's bag is a proper job, and it keeps them warm. An adult looks after the pot on the stove.

Why nobody should eat snow

Eating snow is tempting for children, but it is a poor way to drink. The body has to melt the ice itself and warm the water to body temperature. That costs about 490 kilojoules, or around 120 kilocalories, for every litre. It chills the mouth and throat and takes heat the child needs more elsewhere. Melt the snow in the pot, and give it to the child warm.

When you are heading further out

A night near the car can get by with water from home in flasks. The further out you go, the more of the water has to come out of the snow, and the more fuel has to go into the pulk with your gear. Up on the open fells there is rarely any running water in winter, and the wind makes the stove weaker. How to plan a trip like that is covered in winter camping in the mountains.

The same maths applies if the water goes off at home. How the family copes when the tap stops working is in water preparedness.

Count, choose, melt and save in a single evening

This is what the evening can look like when the water is planned:

• Before you leave: the home test is done, the fuel is worked out and the flasks are filled with boiling water.
• When you arrive: the snow corner is marked out, and the children fill the bag with packed snow while the tent goes up.
• When the stove is lit: first the starter water, then snow a little at a time with the lid on. The water for dinner does not need to be boiled separately.
• Before bedtime: the drinking water is boiled, the flasks are filled and the hot water bottle goes into the sleeping bag.
• In the morning: the bottle gives water for the porridge while the stove melts the day's water for the flasks.

Then nobody has to stand waiting for a splash of grey water at the bottom of the pot when it is dark and minus fifteen.