Experts said the combination of soaring temperatures and the plastic bottle make it a fire hazard.
The risk comes from the bottle of water being left in a car that's in direct sunlight.
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The water and plastic create a magnifying effect that first responders said could set upholstery or a piece of plastic on fire in a couple of minutes, the Atlanta Journal-Constitution reports.
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If you have a bottle of water in your car right now, don't panic.
"The ignition temperatures of those items are about 400 degrees, so it would take some time to achieve that, and you need low humidity, dry heat, but it is possible that it would start a fire," firefighter Jay Symonds told WSTM.
All that considered, it's better to be safe than sorry.
Authorities said it's best to store water bottles in the trunk, as long as it is out of direct sunlight or in a cooler.