Starting a fire with a water bottle follows the same principle of using a magnifying glass to create an intensely focused beam of sunlight on one spot. Of course, this will only work during the daytime, when there is plenty of sunlight. For starting a nighttime campfire, you may need to use other methods. (Related: PREPPING 101: Top 11 ways to start a fire.)
You will need a plastic water bottle. Clear plastic works best for magnifying heat, but you can also use colored plastic bottles if that is all you have. Bottles with bigger curves also greatly improve your chances. The top portion of the bottle should be smooth and round. Make sure your bottle is filled with water, though any other clear liquid should work just as fine. If your bottle has any labels, remove them so they won't obstruct the sunlight.
Next, you will need paper to use as tinder. Computer paper is ideal for this use. For better heat absorption, you will want to use paper that has black ink or any dark colors on it. The darker, the better. If you don't have any paper with dark spots, rubbing the paper with dirt will do. Three sheets of paper should be enough.
Take your first sheet of paper and fold it three times. Make sure to keep enough of the dark area exposed as this will be your platform for the heat to be focused on. Once you are done, set this piece of paper aside. Get the two additional sheets of paper and tear them both in half. This should leave you with four new pieces of paper. Next, you will want to fold each piece in half with the line going down the middle.
The top portion of your water bottle should have a convex edge. Use this convex edge as a substitute magnifying glass to refract the sunlight. Find the precise point where most of the sunlight is concentrated. If you see a focused beam coming out from the other side of the bottle, then you are doing it correctly. Focus this beam of sunlight onto the black area of your folded paper. Begin by holding the bottle near the paper and slowly move it further away. Keep the sunlight focused on the dark area for a few seconds until the paper starts to produce smoke. When the paper starts smoking, keep the sunlight directed at the dark spot until it burns a hole the size of a quarter.
Once your piece of paper has a quarter-sized hole of small embers, insert it into the crease of one of your four previously folded pieces of paper. Grasp the papers together at the corner. Hold it loosely enough to let air flow freely through it but tightly enough that the embers can spread to the rest of the paper. As the embers grow and consume the paper in your hands, add the remaining torn layers of paper until you have used them all. If you've followed the instructions properly, you should now have a smoking bundle of sheets. Blow vigorously on the embers until the flame ignites.
Learn other essential survival skills for when SHTF at Survival.news.
Sources include: