Learn how to boil water using rocks with our straightforward guide. See what rocks to use and how many you’ll need, and how long it takes.
If you ever find yourself out in the wild and in desperate need of water you should never drink it without properly purifying it first.
We’ve talked about purifying water in another post, but today we’re offering a neat little survival tip to boil water when you don’t have a container that can go right into the fire.
If you don’t have a container that you can heat over a fire, you can boil water using rocks.
This simple and ingenious method is ages old. It uses the rocks to transfer heat to the water and ultimately boil the water.
Boiling Water With Rocks
A good rule of thumb is to boil one gallon of water you’ll need about 20 rocks and about 30 minutes of time to heat the rocks, and about a minute to actually boil the water.
Be prepared ahead of time to wait for the rocks to heat, and have enough wood on hand to feed the fire.
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You’ll need some medium sized rocks (see below for what kind you’re looking for), a small fire, a container, and two sticks to use as tongs (or one split stick).
To make a pair of tongs to move around the hot rocks, you can either cut two sticks about the same length and use them like chop sticks, or you can split a 2″ sapling half way down it’s length. Adding vines or paracord near the end of the split will keep the sapling from splitting any further, but it’s not necessary if you’re careful.
Place the rocks in the center of your fire and allow them to heat up and wait. Once the rocks have heated up (to about 1,000F), pour your water into the container and quickly transfer them using your makeshift tongs into the container. Give them a good blow of air to knock off any ash before gently setting them in.
As the rocks transfer heat to the water you’ll hear hissing and see boiling and bubbling. Once a rock quiets down you should wait about a minute longer, by then it’s given it’s stored heat to the water and can be taken out. Do not put it back in the fire, allow it to dry in the sun for another day.
To purify the water keep it boiling for a couple of minutes and stir the water to ensure it all heats evenly. If you’re not in a hurry you can leave the rocks in and allow them all to cool, and then remove the rocks before drinking your water.
For more on the times and temps needed to make water safe, see our post on how long you should boil water.
Of course, you could carry a cheap and dependable water filter with you, such as a Sawyer Mini Water Filter that can filter up to 100,000 gallons of water (lifestraw’s filter about 265 gallons) and removes 99.99999% of all bacteria and 99.9999% of all protozoa quickly and efficiently.
If you’re cooking with the water, remove the stones and add your ingredients while it’s still warm. Stir the water around and keep the temp up by transferring new rocks from the fire to the water as needed. Again, do not add the wet rocks back to a hot fire or they could explode.
Here in this video the process is shown from start to finish.
And here in this video water is boiled inside of a hat, proving that as long as you have a container that will indeed hold water you can purify it for drinking (dandruff and salty sweat included in this case).
You cannot simply pick up any old rock for this survival trick. Get rocks from a high and dry location. Do not use wet rocks, rocks from a river or creek, or any sort of moisture-laden rock as they may explode when heated.
The best type of rocks to use should look plain, dry, and not sparkly. Do not use rocks that are made of crystals, or that are shinny and sparkly.
If you know what you’re doing so you don’t kill yourself…you can collect plants or natural herbs and brew some bush tea with this same method. Make sure you read up on your local plants and know exactly what you’re collecting, eating wild edibles isn’t a time for guessing games.
Try boiling some water with rocks at home before venturing out, it’s pretty fun and interesting. It’s also a neat survival tip to teach the kids.