Gemma del Caño, pharmacist: "Leaving a bottle of water in the sun in the car seems harmless, but it's actually a cocktail of migrated plastics."

During the hottest summer months, it's common to leave a half-empty bottle in the car's cup holder (or anywhere else) only to find it completely reheated hours later, but many people still drink it. This habit, which may seem trivial when thirsty, hides risks related to the release of plastic compounds , bacterial growth, and loss of water quality.

Pharmacist Gemma del Caño, a food safety expert , has warned of the effects of this habit in an article published in Meteored . She explains, "Leaving a bottle of water in the sun in the car seems harmless, but it's actually a cocktail of migrated plastics, microplastics, bacteria, and bad taste." The specialist details seven reasons that support this claim.

The risks of drinking reheated water

The first is the migration of plastic compounds , since at temperatures close to 70°C, polyethylene terephthalate (PET) bottles allow substances that shouldn't be present in the water to pass through. Added to this is the release of microplastics , tiny particles that heat releases from the material and end up floating in the liquid.

Another aspect highlighted by Del Caño is the appearance of a true "bacterial spa." If the bottle has already been opened, the combination of humidity and heat encourages the bacteria in saliva to multiply rapidly, increasing the likelihood of causing digestive discomfort such as gastroenteritis.

The taste is also affected: water can acquire a strange taste due to chemical reactions caused by the heat , to the point of resembling "radiator water." Furthermore, drinking hot water is much less filling and promotes dehydration on days when the body needs proper fluid replacement.

Del Caño adds a sixth factor: the risk of acetaldehyde release under extreme heat conditions. This substance doesn't cause immediate poisoning, but it does impair flavor and isn't recommended in high concentrations. Finally, the expert warns against the false sense of security of those who claim they've done it for years without consequences: toxicity depends on the dose, frequency, and individual susceptibility.

The specialist concludes that the best thing to do is to avoid leaving plastic bottles exposed to the sun , use reusable stainless steel containers, and always prioritize tap water, which is much more economical and environmentally friendly.