Boil water to make it safe

Bring water to a rolling boil — even clear water can carry sickness you cannot see.

easy⏳ an hourtradition — not yet hand-tested

Clear, cold, delicious-looking water can still make you badly sick. The dangers are germs — living things far too small to see — washed in from animal droppings, dead things upstream, or dirty hands. They cause days of vomiting and diarrhea, and diarrhea in the wild is not just miserable: it drains the water out of you faster than you can drink, and that can kill. One hour of boiling discipline prevents almost all of it.

The good news: every disease germ that lives in water dies from heat. You do not need chemicals or filters to kill them. You need a fire, a container, and one simple visual signal — the rolling boil.

You need

• Water — the clearest you can find. Boiling kills germs but does not remove mud or chemicals, so start with the best source you have.
• A fire — steady flames or good coals, enough to keep a pot hot for a while.
• A container that can sit on fire — a metal pot or can is ideal. Scorch off any paint or plastic lining outside your drinking batch first.
• No metal? Then fist-sized dry stones — from a dry hillside, never from a river or damp ground (wet stones can burst in fire). You will heat these and drop them into a wooden, bark, or hide container of water.
• A cloth — to strain cloudy water before boiling, and to cover the water after.
• Two long green sticks — as tongs for moving hot stones, if you use the stone method.

Steps

1. Strain the water through cloth into your container if it is cloudy. This removes dirt and wrigglers, not germs — it just makes the water nicer and the boiling more effective.
2. Put the container on the fire, resting on stones or hung above the flames. Fill it no more than three-quarters full so it does not boil over.
3. Wait for a rolling boil. That means big bubbles rising fast all across the surface, so violently that stirring does not calm them. Small bubbles on the bottom or a gentle shimmer is not enough — wait for the full roll.
4. Hold the rolling boil for one full minute. Count it out or watch it steadily.
   • High in the mountains — roughly above 2,000 metres (6,500 feet) — boil for three minutes instead. Water boils at a lower temperature up there, so give the heat more time.
5. No pot? Use hot stones. Heat several fist-sized dry stones in the fire for about half an hour, then lift them with your green-stick tongs and lower them one at a time into the water container. Keep adding hot stones until the water reaches and holds a rolling boil for a minute. It hisses, spits, and steams — keep your face back.
6. Cover the water and let it cool on its own. Do not add cold untreated water to "speed it up" — that undoes everything.
7. Store it covered and pour, don't dip. Dipping a dirty cup or hand into boiled water re-poisons the whole batch.

Watch out

• "It looks clean" means nothing. Germs are invisible. Boil every drop that goes in your mouth — including water for rinsing food, washing wounds, and brushing teeth.
• Boiling does not fix everything. Salt water, water tasting of fuel or chemicals, and water near mines or sprayed fields stay dangerous no matter how long you boil. Find a different source. Never drink seawater — boiling it makes it saltier.
• Warm is not boiled. The most common failure is impatience: water taken off at "steaming" can still carry live germs. Wait for the true rolling boil.
• River and wet stones can explode in fire. Trapped water inside turns to steam and bursts the rock, throwing hot shards. Use only stones from dry ground.
• Scalds are the everyday injury here. Set the pot where it cannot tip, keep children back, and lift with cloth or sticks, never bare hands.
• Re-dirtying is silent. A fly, a dusty lid, a dipped finger — keep boiled water covered and use it within a day or two, or boil again.

How it works

Germs are made of delicate machinery — proteins — that heat wrecks the way heat wrecks a raw egg: once cooked, it cannot go back. Most disease germs are already dying by about 70°C (158°F), well below boiling. But you have no thermometer, and a rolling boil is one you can see with your own eyes: when the water rolls, you know it got hot enough, everywhere in the pot.