Water from snow and ice

Melting ice takes a surprising amount of energy: melting ice at zero degrees alone costs about as much heat as it would take to warm the same water afterwards from zero to around 80 degrees. That is why it takes so long for snow to become water, and why it uses so much fuel.

Fresh powder snow consists mostly of air. A pot filled to the brim shrinks to a small puddle as it melts. Older, settled snow and firn are denser, and ice is densest. If you can reach clear ice safely, you get considerably more water per potful.

Snow conducts heat poorly. If dry snow lies directly on the hot bottom of the pot, the bottom can overheat while the snow above is still cold. The water then tastes scorched, and thin pots can be damaged. A little water left in the pot spreads the heat and prevents this.

Choose clean, undiscoloured snow away from paths, campsites, toilet spots and animal tracks. Leave yellow, reddish, grey or sooty snow where it is. Near roads, settlements and industry, snow can contain air pollutants and road salt.

Start with some water in the pot and add snow in small portions. Stir, press the snow into the water and put a lid on – that saves a noticeable amount of fuel. Set up the stove outdoors, sheltered from the wind, because wind carries a lot of heat away.

Keep the water you have made liquid. Keep bottles close to your body or well insulated, at night for example inside your sleeping bag. Water freezes from the top: if you store the bottle upside down, the opening stays free of ice for longer.

Never run a stove inside a tent, snow cave, igloo or any other enclosed shelter. Combustion can produce carbon monoxide. This gas has no colour and no smell; poisoning makes you tired and confused and can be fatal without clear warning. Headache, nausea or dizziness while cooking are alarm signs: get into fresh air immediately and, if symptoms persist, call the local emergency number (112 in the EU).

Frozen lakes and rivers are a tempting source of ice, but only if their load-bearing capacity is certain. If in doubt, take snow from the shore rather than ice from the lake.

Eating snow in larger amounts chills the body and costs energy you urgently need in the cold. It is also untreated. When handling hot pots and stoves in thick gloves, make sure everything stands stably: scalds are especially bad in winter, because wet clothing cools you down quickly.

In winter, it is often not water that is scarce but fuel. If you depend on meltwater, plan considerably more fuel than for a summer trip and keep an eye on consumption along the way. A windscreen and a lid make a big difference.

It is practical to combine melting and disinfecting: since the water is on the stove anyway, simply bring it to a rolling boil. That saves a second step. Alternatively you can treat meltwater by another suitable method, such as chlorine dioxide following the manufacturer's instructions – but with very cold water the contact times are often longer.

In sunshine, snow can melt slowly on a dark sheet or in a dark bag. That saves fuel but takes a long time and does not replace disinfection. Hollow-fibre filters are tricky in winter: if water freezes inside their fibres, they can be damaged without any visible sign.

A common misconception is: „Fresh snow is clean, cold kills germs.“ Many pathogens survive freezing, however, and some resistant forms, such as cysts of single-celled parasites, remain infectious for a long time. Snow and ice can also contain soot, air pollutants or animal droppings.

Meltwater is therefore raw water – just like water from a stream. Neither melting nor boiling removes chemical contamination. Glacier streams often carry fine rock flour that turns the water milky; this is usually not toxic but can clog filters quickly.

In winter too, the body loses a lot of water through dry, cold breathing air and through sweating under warm clothing. Warm drinks made from meltwater help twice over: they provide fluid and a little warmth.