system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why will water start to taste bad when you leave it in a glass for too long, but will taste fine when you dispense it out of a tap where it's been sitting for months?

If you leave water in a ceramic, glass, or cup it will start to taste bad after a day or two, even if it's covered with a lid. However, when we pour water out of a tap into a glass it will taste fine, even though it's been sitting for days/months in a water reserve tank. Why is this the case?
gpt
Normally, water has a bunch of dissolved gases in it, as well as dissolved minerals that can react with oxygen. Inside the pipe/tank, those gases have nowhere to go and there's no oxygen to react with, so the water doesn't really "age". As soon as you sit it out in the open the dissolved gas mix changes and any reactions that need oxygen to proceed can get going. There's enough of that going on in most water to change the taste enough to notice.