A garden full of snow looks like a solved water problem. It is not, quite. Snow is mostly air, and turning it into water costs a surprising amount of fuel at exactly the point in a winter emergency when fuel is the thing you are rationing.
Worth doing, worth doing properly.
How much water is actually in it
A full 10 litre bucket of ordinary snow gives you about a litre of water. That is the number worth internalising, because it changes how many trips you plan and how much fuel you budget.
Ice is dramatically better on every count: it yields nearly its own volume, and because it conducts heat far better than snow it melts faster for the same fuel. If there is ice available, from a frozen butt, a pond edge, or icicles, take the ice first and leave the snow.
Never eat it
The starter-water trick
Putting dry snow into a dry pot over heat is the classic mistake. Snow is a poor conductor, so the snow touching the metal melts, the rest bridges over the gap, and the pot scorches with nothing in contact with it. On a lightweight pot you will burn through it. Everything then tastes of scorched metal.
Always start with a few centimetres of liquid water in the pot. Keep back a cupful from the last batch specifically for this. Add snow to the water a handful at a time, letting each addition melt before adding the next, and keep the pot at least a third full of liquid throughout.
If you have no water at all to start with, add snow very slowly, keep the heat low, and stir constantly until you have a liquid base to work from.
Two more things worth knowing:
- Compact the snow before it goes in. Squeezing it into a snowball first gets far more mass into the same pot volume and cuts the number of cycles.
- Keep a lid on it. Melting snow with the lid off wastes a large share of the heat and loses water as steam.
Choosing what to melt
Snow is not sterile. It is condensed atmospheric moisture that has fallen through whatever is in the air and then sat on whatever it landed on.
Take it from a clean, undisturbed surface well away from:
- Roads and pavements, which means road salt and vehicle residue.
- Roofs, unless you already collect from them and know what they are made of.
- Anywhere animals have been. Discoloured snow of any shade goes unused, no exceptions.
- The top surface after a still, dry spell, which collects deposited dust and soot.
Dig down and take clean snow from below the surface crust, not the top layer.
Then treat it as you would any surface water. Melting is not disinfecting: it happens well below the temperature that kills anything. Filter it if it is visibly dirty, then boil it or dose it with bleach at the ratios on the water page. If you have already built a biosand filter, meltwater is exactly the sort of low-sediment input it handles well.
The one genuine bonus: meltwater from clean snow is very low in dissolved minerals, so it is kind to a hollow-fibre filter and will not scale a kettle.