Survivalist Bear Grylls always talks about how finding water is one of the key priorities of survival. But when you do find water, you need to be able to filter and purify it—and boiling is a good way to purify it. You can also cook things in boiling water to kill two birds with one stone.
Use a storm kettle
If you have a storm kettle, you’re in business. The most well-known are called Kelly Kettles, and some are small and light enough to carry on a trail.
The kettle is a hollow metal cylinder that acts as a chimney. The water goes into the skin of the cylinder, and a fire is lit at the base using twigs or whatever handful of fuel can be found. The water takes just a few minutes to heat.
Use a plastic bottle
Unfortunately, it’s not difficult to find an empty plastic bottle littering a trail or shoreline these days, but clean ones can be very useful. Fill the bottle with clear water and put the cap back on. “If your bottle is really full, it will act like a pressure cooker and boil faster,” says Bear in Extreme Food.
Light a fire and then make a little tripod over it. Hang the bottle over the fire with some cord, but not too low into the flames where it will melt.
“If you get the height just right—it will depend a bit on how hot your fire is, and you should let the bottle swing a little so that it doesn’t get too hot in one place—you will find that as it comes to the boil, the water will stop the plastic bottle from melting,” says Bear.
The plastic can potentially release certain chemicals into the water, so Bear advises that this is for a survival situation only, rather than something to do regularly.
Use a birch-bark pot
Birch trees,identified by their white, papery bark with horizontal black markings, can come in very handy for survival. Fashioning a birch-bark pot offers a clever way to boil water.
Get a roughly rectangular piece of birch bark, around the size of a piece of printer paper, and fold all of the sides up and inwards to create a basket or shoebox shape. The diagonal folds at the corners should crease inwards.
Using the split ends of some small sticks, make some pegs to hold the folds in place. Fill your makeshift pot with water and put the whole pot onto the embers of a fire, but not onto the flames. The water inside should stop the birch from burning as it comes to a boil.
I always encourage my scouts to carry an un-insulated (not double walled, vacuum insulated, etc.) metal water bottle (pick them up from thrift stores for cheap) and they can boil the water like the storm kettle right over a camp fire.