I know it's hot out and you might be leaving plastic water bottles around your car, but some fire departments are warning you that it might not be a good idea. This comes from a WILX affiliate, as they say leaving plastic water bottles in your car during extreme heat with direct sunlight may cause a fire. The fire fighters go on to explain that the bottle has to be full or almost full and has to have direct sunlight for a minute or two to start a fire.

The reason for the water bottle catching fire is that the water and plastic create a magnifying effect, which could then set the inside of the vehicle or a piece of plastic on fire. The better idea would be to leave water bottles in the trunk as they will stay cooler because they are away from sunlight.  Now it's not going to happen 100% of the time, but there is no need to risk it. Plus, leaving water in your hot car during a 90+ degree day is going to make the water hot and not really quench your thirst. More on it here.