Firefighters are warning people to not leave plastic water bottles in cars during extreme heat. They say leaving a plastic bottle of water in a hot car in direct sunlight can start a fire in just minutes. In order for that to open, firefighters say the bottle would have to be full. Then, the water and plastic could create a magnifying effect, which could essentially set the inside of the vehicle or a piece of plastic on fire. Firefighters suggest putting bottled water in the trunk instead if it has to be kept in the vehicle.