Taking enough water with you on hot days is always a good plan. But don’t be a cowardly drinker and drink the last bit of water before you leave the car. Not only is the water filthy hot when you get back, it can be quite dangerous to leave a water bottle in the sun. The shape of the bottle of water and the liquid act like a magnifying glass and bundle the light rays. It can get very hot under the light beam, resulting in burn holes. If it remains in place for too long, the car can catch fire. Below you can see how easy it is.