Some first responders are warning drivers about leaving water bottles in their car.

They say that leaving a plastic bottle of water in a hot car in direct sunlight can start a fire in just a couple of minutes.

One firefighter upstate tested the theory - and says it's no myth.

"The water in the plastic creates a magnifying effect,” says firefighter Jay Symond. “It can essentially set upholstery on fire or a piece of plastic on fire."