Leaving Bottled Water in the Car Can Be Dangerous

Leaving a bottle of water in the car is a habit of most drivers. However, in reality, bottled water can also cause fire or even explosions if placed in certain spots during hot weather.

In the summer heat, almost everyone carries a bottle of water to avoid the hassle of having to buy drinks under the scorching sun. If you own a car, chances are high that you have the habit of keeping bottled water inside, often on the dashboard or next to the driver’s seat for convenience.

In an experiment conducted by Dioni Amuchastegui, an electrical engineer in Idaho (USA), a water bottle was shown to focus sunlight and create heat exceeding 100°C. When placed on a dark surface, such as a car seat, the heat generated was enough to ignite a fire and cause a disaster.

In fact, a fire caused by a water bottle inside a car requires multiple factors, but that doesn’t mean it can’t happen. Amuchastegui himself nearly experienced such an incident before deciding to run the experiment as a warning to others.

If the temperature is normal, this isn’t a problem. But if your car is parked outside under the midday sun, you need to think twice. That harmless-looking bottle of water can literally turn your car into a “fire car.”

The reason is that water bottles are usually spherical in shape and made of transparent plastic. With water inside, the bottle can act as a magnifying glass. Under midday sunlight, car interiors can heat up to nearly 60°C. Sunlight passing through the bottle can focus on one point, pushing the temperature even higher.

Many people admit they used to put water bottles on car seats without ever realizing how serious the consequences could be. Moreover, car experts point out another danger: if the bottle rolls off the passenger seat, it could get stuck under the accelerator or brake pedal. Imagine a bottle wedged under the brake when you need to make an emergency stop—that would be extremely dangerous.

Another related concern is health. Research has shown that drinking water from plastic bottles left in high temperatures for a long time can cause harmful effects on health.

The study specifically highlights cases where bottles had been left for months behind car seats, and when drivers got thirsty, they would drink from them. This small act, seemingly harmless, can silently damage health over time.

According to this study, when outside temperatures range from 80°F (27°C) to 100°F (38°C), the temperature inside a car without air conditioning can reach 130°F (54°C) to 172°F (77°C)—even hotter than a low-setting oven.

Research from the American Academy of Pediatrics also found that the difference in temperature is minimal whether the car windows are closed or slightly open. In both cases, the interior temperature can rise to about 40°C within an hour, even when the outside temperature is only 22°C.

Therefore, it’s best to abandon this habit before it’s too late. If you must leave water in the car, at least make sure it’s sealed and stored in a shaded place, away from direct sunlight.