Why does my 4L bottle of water have a Best Before date on it? How does water deteriorate?
The plastic will eventually cause a minor chemical reaction and slowlyDeteriorate into the water.
A lot of bottle water has no chlorine and will grow bacteria.
nature has its own way to keep water fresh in river, oceans, spring falls..... but when we preserve it in plastic bottle....it expires or lost its taste...as other food items, juices, cans.. preserved items are good only before the expiry date.
if its fortified with certain minerals it could eventually go bad, and unsealing any container can cause air to get in with bacteria, etc. you shouldn't really worry a whole lot with water tho
I agree with Tb23