* Safety: The water itself won't become unsafe to drink in the sense of being contaminated with harmful bacteria or viruses. The plastic bottle is a barrier against that.
* Taste and Quality: The heat will accelerate the leaching of chemicals from the plastic bottle into the water. This can affect the taste, making it unpleasant, and potentially introduce microplastics. The heat can also cause the water to taste less refreshing and potentially develop an off-flavor.
* Bottle Integrity: Extreme heat can cause the plastic bottle to warp or even leak. If the bottle is visibly damaged, it's best to discard it.
In short: While not inherently dangerous, water left in a hot car will likely taste worse and may contain more microplastics. It's best to avoid drinking it if possible, especially if the bottle has been exposed to excessive heat for a prolonged period. It's always safer to opt for a fresh, cool bottle.
