Health risks of drinking water left in plastic bottles inside cars

Leaving plastic water bottles inside a vehicle can pose potential health risks due to heat exposure and plastic degradation. When single-use PET (polyethylene terephthalate) bottles are subjected to high temperatures within a parked car, the plastic can begin to break down at a molecular level.

This process can cause chemicals, such as antimony and trace plastic substances, to migrate into the water. Vehicles can act as heat traps, with internal temperatures reaching between 50–70°C, which accelerates the chemical instability of both the plastic and the liquid.

Additionally, once a bottle has been opened, it is no longer sterile. The combination of heat, moisture, and air contact inside a warm vehicle creates an environment favorable for bacterial growth, particularly if the bottle is reused or not consumed immediately. Changes in the taste or aroma of the water serve as indicators of these chemical changes or plastic degradation.