system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why does my cup of water that was left out during the night taste bad the next day?

What happens in there. I have a full cup of filtered water sit out over night. then the next day at any time it tastes very weird. Why is that?
gpt
The water will also absorb odours from the air. 
It used to be a painters' trick to leave a bucket of water in a newly decorated room. The water would absord some of the paint smell and solvents from the air.