The next time you pull into your driveway, grab your bag, keys, and phone–and your water bottle, too.

While most of don’t think twice if we leave a bottle of water in the car overnight, firefighters and other safety advocates are warning drivers that this seemingly innocuous act can actually create a serious fire hazard.

It may be surprising to learn that water—which is typically used to put out fires—can lead to flames, but in a test conducted by Oklahoma's Midwest City Fire Department, sunlight magnified by a water bottle reached 250 degrees, news channel KFOR reports. "The sunlight will come through, when it's filled with liquid, and act as a magnifying glass as you would with regular optics," fire fighter David Richardson said in the report. "It uses the liquid and the clear material to develop a focused beam and sure enough, it can actually cause a fire, a combustion."

The fire risk has flown under the radar for a long time, but now there is a national effort to make people aware of this surprising fire hazard. Idaho Power posted a video to their Facebook page demonstrating the magnification power of a bottle of water. The video featured an Idaho Power employee who had an eye-opening experience that he wanted to share. He was on his lunch break when he noticed smoke coming from beneath the center console of his truck. "I looked over and noticed light was being refracted through a water bottle and starting to catch the seat on fire," Dioni Amuchastegui said in a video shared on the company's Facebook page last year. He removed the bottle and solved the problem before there was a more serious fire. He learned a valuable lesson and was willing to pass it on.

The good news is that this is an easy fire to prevent. Bring your bottled water in—or even better, use a reusable bottle with opaque sides that won’t turn into a mini magnifying glass if you leave it in the car.