Does water have an expiry date?!
Answers: How long does clean water last? What happens to it if left out?
It is weird - water can go stale. Take a glass of water - room temp - drink some, then leave it out overnight and try it the next day. It has a stale taste to it.
If you have a tightly sealed container stored in a cool place. It can last forever. Water not sealed tightly (air tight) can get containments in it and you wouldn't want to trust the water. You may get sick - It is all how you store it. If you don't know something about it don't trust it. You can always boil water and have it evaporate into another container or add a small amount of bleach in it to clean it. then it can br drinkable. Keep in mind adding bleach kills bacteria but will make it taste funny. There are kits out there that test water for people, they are in survival kits. They are the best way to go if unsure about water. However, if you live where there is water, throw away the stuff if you don;t know and just use the water that you can trust.
If you leave water out that you drank, it will grow bacteria from the germs inside it.
Usually, bottled water has a date that signifies the "best by" date. After this date, water will begin to loose it's flavor, but as long as the bottle remains unopened, it'll pretty much last forever.