I stumbled upon this old article (Why You Should Never Leave A Water Bottle In A Hot Car). It turns out that your bottle of water can act like a magnifying glass.
The article states that sunlight magnified by a water bottle can reach a temperature of 250 degrees Fahrenheit. David Richardson of Oklahoma’s Midwest City Fire Department explains that as sunlight passes through the clear plastic bottle and is bent by the water, a focused beam of light is formed. “It can actually cause a fire, a combustion,” he said.
This gave me some idea about interesting ways this could play out in a story.
Maybe it’s a team prank gone wrong when the players fill the coach’s car with water bottles and end up setting it on fire.
A teen uses water bottles instead of the usual fire starters leaving arson investigators scratching their heads.
Someone cleans their girlfriend’s or boyfriend’s prized or brand new car in an effort to apologize and leaves two water bottles inside as a kind gesture, which inadvertently ends up setting fire to the vehicle.
Who wants to talk more about how you can use this idea in your current or next story?