An Idaho Power technician found himself not in, but near, hot water in the sweltering heat of his work truck earlier this summer.
Dioni Amuchastegui was taking a lunch break in his truck when he noticed something peculiar. The Idaho Power professional explained what happened in a 
“[I] happened to notice some smoke out of the corner of my eye. I looked over and noticed that light was being refracted through a water bottle and was starting to catch the seat on fire.”
This is the same principle as starting a fire by focusing a beam of sunlight through a magnifying glass onto a pile of dry leaves or twigs.
Eventually the kindling gets so hot that it ignites. The video shows Amuchastegui reproducing the effect and measuring the temperature of the concentrated light with a heat gun.
On the video, the temperature topped out at 213 degrees.
Richard McKinnies, who runs Idaho Power’s garage, closed the video by reminding drivers that it’s important to keep water handy during the hot summer months, but, “If you have [a water bottle] in the cab of the truck, just keep it out of the sun.”
You may want to go ahead and take it inside, though.
Still, fire isn’t the only thing to worry about. Researchers from both the University of FloridaIdaho Power/Facebook
and University of Cincinnati have researched the effects of heat on water bottles. Unfortunately, the results don’t look good for people who regularly leave plastic bottles in their cars.
In both studies, scientists found that exposure to heat can significantly increase the volume of the potentially harmful chemical bisphenol A (BPA) that is released into the water by plastics.
“There is a large body of scientific evidence demonstrating the harmful effects of very small amounts of BPA in laboratory and animal studies, but little clinical evidence related to humans,” Dr. Scott Belcher of the University of Cincinnati explained to Science Daily.
Don’t get too comfortable. Belcher continued, “There is a very strong suspicion in the scientific community, however, that this chemical has harmful effects on humans.”
University of Florida soil and water science professor Lena Ma observed various brands of water that were stored in hot places for a month. When stored for four weeks at temperatures close to 150 degrees, the volume of BPA released increased more than tenfold.
A month straight of extreme temperatures may seem impossible.
But it doesn’t have to be 150 degrees outside for your car to feel the heat. A 2003 Centers for Disease Control and Prevention study noted that the average car warms up more than 43 degrees within an hour of being parked in the sun.
And it’s not just disposable, sealed bottled water than can be dangerous. Dr. Belcher studied hot water’s effect on Nalgene bottles and similar products and found that with cool or room-temperature water, the amount of BPA released from these bottles was not particularly startling. When those same bottles were exposed to boiling water, though, “the speed of release was 15 to 55 times faster.”
If you need a refresher on the boiling point of water, it’s 212 degrees. The water in the video, of course, hit 213. The takeaway is clear: Unless you want to risk setting your car on fire and being exposed to potentially harmful chemicals, always take your water bottle inside with you.