Other than the fact that the water will be warm (not very appealing on a hot day), there's another reason to keep your water bottles in the shade.

It's not the danger of bacterial growth (although that can happen once the bottle has been subjected to a sip or two). It's something called bisphenol A (commonly abbreviated as BPA).

And furthermore, it's not the sunlight that causes the problems.

A study done by the University of Florida found that if a plastic water bottle is exposed to long periods of heat, it can release bisphenol A and the chemical element antimony into the water.

Why is that a bad thing? Mashed.com explains:

Researchers have suggested that BPA has been found to change hormone levels, lead to cardiovascular issues, and even increase the risk of some cancers. Introducing antimony into your system can lead to a range of gastrointestinal issues including diarrhea, vomiting, and stomach ulcers.

The study measured the levels in bottles that were kept at a temperature of up to 158 degrees Fahrenheit and found that the higher the temperature, the higher the levels of BPA and antimony in the water. This means doesn't have to directly be in the sunlight, but instead it's the associated temperature that causes the plastic to leach impurities into the water.

If you've ever wondered why water bottles feature an expiration date, it's not because the water "goes bad." It's because of the dangers of BPA  co-mingling with your water.

The story goes on to point out that if you observe the expiration dates and keep your water bottles out of extreme heat, you should be just fine.

My dog Buddy prefers this alternative to single-use water bottles. As a child of the 1960s and 70s, I'm with him:

Riley O'Neil, Townsquare Media