You have to be sure that the sun never focuses through the bottle into a point on anything that burns.
Water bottles make magnifiers, you can start fires with them. They aren't ideal but it does happen by accident from time to time.
People have set cars on fire by leaving a bottle of water laying on the rear dash of cars.
Water bottles make magnifiers, you can start fires with them. They aren't ideal but it does happen by accident from time to time.
People have set cars on fire by leaving a bottle of water laying on the rear dash of cars.