As summer cranks up the heat across much of the country, staying hydrated becomes an everyday priority. While it’s second nature to tote around a water bottle, there’s one place firefighters say it definitely shouldn’t be left: your car.
That innocent plastic bottle rolling around in the cupholder? It might pose more than just an eyesore. In very specific conditions, it can act as a magnifying glass, concentrating sunlight into a powerful beam capable of scorching car interiors — and potentially even starting a fire.
A Startling Lunch Break Discovery
Back in the summer of 2017, Dioni Amuchastegui, a battery technician working for Idaho Power, stumbled upon a scene that caught him completely off guard. Taking a break in his vehicle, he spotted smoke wafting from the center console of his truck.
“At first, I thought it was just dust catching the light,” Amuchastegui explained in a 2017 interview. “But my windows were up. There wasn’t any airflow.”
A second glance revealed the true culprit: sunlight refracting through a plastic bottle filled with water. That beam of concentrated light had begun to burn holes right into the truck’s seat. Although he reacted quickly and moved the bottle before the situation escalated, two noticeable burn marks were left behind.
Curious — and a little astonished — Amuchastegui decided to recreate the event safely with colleagues at Idaho Power. Their demonstration, which was later posted on Facebook, showed how quickly the heat generated from a sunlit water bottle could cause damage.
A Viral Warning Shared Nationwide
That unexpected experiment didn’t go unnoticed. The video circulated widely and eventually caught the attention of the Midwest City Fire Department in Oklahoma. The department used it as a cautionary example during the hottest months of the year.
While they emphasized that the danger is relatively low, the incident served as a reminder of the odd ways sunlight can interact with everyday objects.
“The conditions need to be quite specific,” explained David Richardson, the department’s spokesperson. “The bottle has to be transparent, contain clear liquid, and be placed in direct sunlight at just the right angle. It’s rare, but definitely not impossible.”
The shape of the bottle matters, too. A curved surface — typical of most disposable bottles — can bend sunlight inwards, much like a magnifying lens. On a clear, sunny day, if that beam focuses onto a dark surface like upholstery or leather, the temperature can soar rapidly. In some instances, concentrated heat can exceed 400 degrees Fahrenheit within seconds. That’s enough to leave scorch marks — or worse.
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Science Behind the Singe
The mechanism behind this surprising phenomenon is all about light and optics. Just like you might use a magnifying glass to ignite dry leaves, a clear water bottle can mimic that effect under ideal circumstances.
As sunlight streams through a car’s windshield, it passes through the bottle and refracts off the water’s surface. If the curvature is just right, that refracted light focuses into a hot point. This isn’t just theoretical — both Amuchastegui and the fire department were able to replicate the effect. In one test, all it took was a water-filled bottle and a dark-colored sheet of paper.
Within moments, the paper began to smoke.
“People don’t usually associate a water bottle with fire risk,” Richardson noted, “but under the right setup, it becomes a very effective lens.”
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It’s Not Just About Fire: Other Concerns With Bottled Water in Cars
Even if a blaze doesn’t break out, there are still reasons to avoid leaving bottled water in a hot vehicle. Extended heat exposure can cause the plastic to break down, possibly leaching chemicals into the water. While research varies on the long-term health effects, the general recommendation is to avoid drinking bottled water that has been sitting in the heat for hours on end.
Reusable bottles made of stainless steel or BPA-free materials are a safer and more sustainable option, especially if you’re frequently on the go. Plus, you’ll be doing the environment a favor while cutting down on single-use plastics.
Fire Prevention Tips From the Experts
Firefighters say that while the water bottle scenario is unusual, it fits into a broader theme: hot cars can become dangerous in surprising ways. Here are a few practical tips to keep both you and your vehicle safe during the hotter months:
- Take It With You
If you bring a water bottle into the car, make sure to take it back out when you leave. Not only will you avoid potential fire risks, but your drink will also stay cooler longer. - Switch to Opaque or Insulated Bottles
Stainless steel bottles or those with solid colors don’t refract light the same way clear plastic does. They also tend to maintain your water’s temperature more effectively. - Avoid Direct Sunlight
If you must leave a bottle in the car temporarily, tuck it under a seat or in a shaded area where sunlight won’t strike it directly. - Monitor Vehicle Temperatures
Remember, interior temperatures can skyrocket during summer. Even if there’s no fire, prolonged heat can damage electronics, melt objects, and create other safety concerns.
An Unlikely Threat That’s Worth Remembering
Though fire outbreaks caused by water bottles are extremely rare, the possibility is no longer just a myth. As with many safety hazards, it’s the unusual ones that catch people off guard.
“What surprised me most,” Amuchastegui admitted, “was how quickly it happened. You just don’t expect that kind of danger from something so harmless-looking.”
While there’s no need to panic or toss out every water bottle, awareness is key. Recognizing how seemingly mundane objects can interact with their environment can help prevent minor damage — or a major headache.
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Quirky, But True
Fire safety often brings to mind images of campfires, candles, or faulty wiring. But now, thanks to one battery tech’s curiosity and a sunny lunch break, we know that even a half-empty bottle in the passenger seat can turn into a lens-shaped heat source.
So the next time you step out of your vehicle on a hot day, take a moment to scan your seats — especially if there’s a clear bottle catching the sunlight. It might just save your seat from a surprise burn mark — or prevent your car from becoming the subject of the next viral fire safety video.
Bottom Line? Keep Your Hydration Handy — Just Not in the Sun
While this phenomenon doesn’t rank high on the fire department’s list of frequent hazards, it’s real enough to warrant a little caution. It’s a weird, rare, but very possible event — the kind that makes summer safety guides a little more interesting.
So go ahead, stay hydrated. But do your car (and your seat cushions) a favor, and leave the bottled water for the cupholder only when you’re inside — not parked and baking under the midday sun.
