How to Purify Rainwater Using Rocks

Heating up rocks is a great way to purify rainwater if you are in need of clean drinking water. Knowing how to kill bacteria and parasites in collected rainwater is an important skill for traveling or camping. If you do not have access to a fire-safe container, you will have to raise the temperature of the water using rocks. Boiling water may not kill everything in it, but it greatly reduces the risk of getting sick from drinking it. You will need access to fire to perform this task.

Things You'll Need

• 1 gallon or less of rainwater
• Container
• Fire pit
• Logs
• Kindling
• Matches or lighter
• Rocks
• Sticks or long spoon

Instructions

1. Collect rainwater in a bucket or other container. You should have a gallon or less in order to make boiling it easier.

2. Collect palm-sized stones. You will need at least 30 of them. Basalt rocks or other types of smooth stones work best. Wash any dirt or insects off of them.

3. Start a fire and drop some large (palm-sized) stones into the fire. Let them heat up for 10 minutes to get red-hot. The rocks should heat up to over four hundred degrees.

4. Remove one of the rocks from the fire using two sticks or a long spoon and drop it directly into the container full of rainwater for 10 seconds. The water will start boiling immediately.

5. Remove the rock from the water and drop it back into the fire. Immediately take another hot stone from the fire and drop it into the container for another 10 seconds. Continue this procedure for at least five minutes, using 30 rocks total. Allow the water to boil for at least five minutes for best results. Keep the water boiling for up to 20 minutes if you have enough hot rocks to add.

Tips & Warnings

• Basalt rocks are the best kind of rock to heat, since they rarely crack due to temperature.

• If your rainwater container is flimsy and made of thin plastic, you should be careful not to melt the plastic with the hot rocks.

References

• Wildwood Survival: Water Purification