Remember in school where we had the experiment of using a magnifying glass, with the sunlight going through it onto a sheet of paper and the the paper would burn? It seems a water bottle can do the same thing.

Firefighter David Richardson of the Midwest Fire Department in Oklahoma talked with KFOR said, "The sunlight will come through, when it’s filled with liquid, and act as a magnifying glass as you would with regular optics. It uses the liquid and the clear material to develop a focused beam and sure enough, it can actually cause a fire, a combustion."

Idaho Power workers saw this first hand.

They posted a video of what the sun can do through a water bottle after a small burn was discovered on the seat of one of their vehicles. In the video, they hold a bottle over the seat and it begins to smoke and reaches a temperature of 213.

The moral of this story, have your water on hand to keep your cool in the heat, just don't leave in your car when you're through with your commute.