Here's a summer safety hazard you'd never think of. Leaving a half-full bottle of water in your car could start a fire. If you don't believe it, there's plenty of video evidence to back it up. Here's how it can happen.

When the sun hits a plastic bottle at the right angle, the water in there can act like a lens, and concentrate the light on one specific point.

It's exactly like that kid who burned ants with a magnifying glass. Under the right conditions, that pinpoint of light can cause smoldering, or worse. A group of firefighters in Oklahoma posted a video last year that shows how it can happen:

The odds of a water bottle setting your entire car on fire are pretty low. In most cases, the worst thing that'll happen is it might melt a small hole in your upholstery.

But if the bottle happens to be next to something flammable, it could start a fire. So if you currently have a bottle of water sitting in your car next to some dry tinder and say, an open can of gasoline, you might want to go deal with that.

Read more at KFOR.