Originally Posted by DevaMajka
I totally had no idea that could happen! Do you mind if I ask how you know for sure it was from the water bottle? I drink day old water occasionally- I'm a little bit freaked out now.
If you've had your mouth on the bottle or container, then organisms from your mouth are left behind in the water. If the bottle is then left in a warm place, or left for a long period of time, those organisms can probably breed and grow. Most of the time, they're harmless organisms, or there's not so many of them, but theoretically I think it's possible to get molds or bacteria in there that might make a person sick.
It's the same reason bottlefeeding mamas are advised to throw away formula after an hour, once baby has had his/her mouth on the bottle-- because the formula is an ideal medium for yuckies to grow in.
It's never happened to me, though.