Summer heat usually means making sure you're well-stocked on water to prevent dehydration. But firefighters are warning that you shouldn't leave plastic water bottles in your car — they can actually cause a fire. 

When a water bottle is left in a hot car, the sunlight can come through the bottle and create a magnifying glass. The focused beam can then cause a fire on your car's interior fabrics. You can see a video of how it happens on Idaho Power's Facebook. 

A test at the Midwest City Fire Department in Oklahoma found that sunlight through a bottle of water reached 250 degrees. 

Fire officials recommend taking water bottles out of the car when you leave or storing them out of direct sunlight. The risk is low, but better safe than sorry. 

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