Water does expire. If you leave it exposed to the air shit will grow in it, and even if you have it in a container you shouldn't keep it for more than 6 months (or if you do, treat it with bleach before drinking it)
My family thinks I'm insane because I almost exclusively get bathroom sink water where I live when I get water. It's so much better than the kitchen taps.
Only problem with water is that I need to get better about actually remembering to drink enough.