system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does bottled water contain sodium?

Does all water contain sodium or is it just bottled? And why is it in there?
gpt
Unless it's been distilled, then sodium \(and other ions\) are pretty much always present in water.  Depending on where the water came from, they could have been absorbed from rocks or soil that the water touched, or from contact with living creatures like plants or animals.  Sodium dissolves in water very easily, so if water contacts any sodium it will take some of it.  Sometimes sodium is added on purpose to affect the hardness or the flavor of the water.