Here's a summer safety hazard you'd never think of. Leaving a half a bottle of water in your car could start a FIRE. And 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 focus the light on one specific point.
Kinda like when you use a magnifying glass and pinpoint the light in one spot which can cause smoldering, or worse.
Now 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.