What happens if you drink water from the plastic bottle left in the car for days?

Most of us leave a plastic water bottle in the car or drink from one that’s been sitting in the sun. It feels harmless. But research shows it could actually harm your health in several ways; from affecting hormones and metabolism to reducing sperm health in men. A study by the National Institutes of health supports this. Researchers gave bottled water to three groups of rats: one group drank cold water from the fridge, another drank water kept at room temperature, and the third group drank water from bottles left in a hot car. The results were clear, rats that consumed the heat-exposed bottled water showed troubling health changes.

• Lower testosterone levels

• Reduced sperm count

• Unusual weight changes

•  Signs of stress and inflammation in their blood

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Scientists found more harmful chemicals (like BPA and antimony) in the hot-stored water, both of which are used to make plastic. These chemicals can leak into the water when bottles are exposed to heat.

Moreover, Dr Parul Purohit, Microbiology resident, Doctor Sampurnanand Medical College, Jodhpur, says the issue isn’t only about plastic alone.  Once you drink directly from a bottle, the bacteria from your mouth go back in. “And if you leave that bottle in a hot car, those bacteria can cause harm. It becomes like a mini incubator,”

Here’s why Dr Purohit advises against drinking from that bottle left in the car, suggests tips to avoid harm: 

• Heat turns your bottle into a mini germ incubator

A parked car can heat up to 50–70°C on a sunny day. “If you've already sipped from the bottle, germs from your mouth, like bacteria and yeast, can sneak back into the water. Warmth gives them the perfect setting to grow fast,” Within hours, the water can become a breeding ground for microbes. “People think it's just warm water, but actually, it's warm, germ-filled water," says Dr Purohit

• Bacteria build a home inside the bottle

Over time, bacteria don't just float around in the water, they stick to the inside of the bottle and build a slimy layer called a biofilm. “This film protects them and makes them harder to wash away. Even if you rinse the bottle, these germs might stay hidden and multiply again,” informs Dr Purohit.

• Mould and algae can grow too

If the bottle is left for days, especially under sunlight, you may end up with invisible fungi like Aspergillus or Fusarium growing inside. These thrive on moist, warm surfaces. While you might not see them, they can still make their way into your body and cause health problems.

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• Even dead bacteria leave behind toxins

One might think at least the germs die in the heat. “However, the worst part is that even dead bacteria can be harmful. As they break down, they release toxins that can irritate your gut and cause discomfort, bloating, or even mild infections,” says Dr. Purohit, adding, " It's not just about live germs. What they leave behind can still harm your stomach,”.

Tips to avoid harm

• Don’t leave water bottles in the car, sun, or warm places
• Keep them in the fridge whenever you can
• Avoid reusing bottles you’ve already drunk from
• If a bottle smells odd or has been sitting too long, just throw it.

Disclaimer: This article, including health and fitness advice, only provides generic information. Don’t treat it as a substitute for qualified medical opinion. Always consult a specialist for a specific health diagnosis.