Drinking water throughout the day is important (especially during the warmer months), and having a bottle on-hand during your trips is smart, but when you exit the car, take that water bottle with you!

Water that has been left in a car on a hot day is dangerous for two reasons; the first is that the hot plastic could cause the chemicals to filtrate into the water. Professor of biochemistry and molecular biology, Cheryl Watson, told Today: “When you heat things up, the molecules jiggle around faster and that makes them escape from one phase into another. So the plastic leaches its component chemicals out into the water much faster and more with heat applied to it.” That said, the publication notes that the International Bottled Water Association disagrees, instead claiming that bottled water is safe in a number of conditions, including being left in hot places like cars.

This brings us to the second reason then; leaving a bottle of water in a car could cause a fire.

Many people are not aware of this risk, because you don’t exactly think that water is capable of causing a fire, but according to Reader’s Digest, this has to do with the shape of the plastic bottle. When the sunlight shines through the window, through the full water bottle, it concentrates the heat and light into one place. Think of it as a magnifying glass, and if the sunlight hits at the right angle, the spot where the light is directed could get hot enough to cause a fire.

Channel KFOR (via Southern Living) reports that sunlight, when magnified by a water bottle, can reach temperatures of 250 degrees. Firefighter David Richardson explained this in more detail, saying, "The sunlight will come through, when it's filled with liquid, and act as a magnifying glass as you would with regular optics. It uses the liquid and the clear material to develop a focused beam and sure enough, it can actually cause a fire, a combustion."

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