The Science Behind the Hazard

If the weather is mild, leaving water in the car is not an issue. But when your vehicle is parked under direct sunlight at noon, it’s a different story. That seemingly harmless bottle of water could literally turn your car into a “fire car.”

The reason is that water bottles, usually spherical in shape and made of transparent plastic, can act like magnifying lenses. When filled with water, they are capable of focusing sunlight into a single point. At midday, the temperature inside a car can reach nearly 60°C. With sunlight passing through the bottle and converging on a spot, the heat can rise even higher, creating a fire hazard.

Temperature Dynamics Inside Your Vehicle

Another study by the American Academy of Pediatrics found that as time passes, the temperature difference inside cars remains minimal whether the windows are completely closed or slightly open. In both cases, the temperature inside can increase by about 40°C within one hour, even if the outside temperature is only 22°C. This rapid temperature rise further exacerbates the risk of fire when combined with the effects of sunlight on a water bottle.