There are two basic ways to start a fire – using friction or using a lens to focus the sunlight. The friction based methods involve a large amount of physical effort. If you prefer to let the sun do the work for you (and you don’t have a magnifying glass), this hack is for you.
Take a piece of paper and turn it into a fire platform by folding it three different times. Next, use the convex edge of the water bottle as a makeshift magnifying glass to focus the sunlight. When the sunlight burns a hole about the size of quarter, add multiple layers of paper over the top of the hole. Swinging the paper around gently will flow air into the embers, causing a fire to form. It’s easier to create a fire if you use paper with big black letters or pictures, because the dark color absorbs heat better.