system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why does water have an expiration date?

Why does *bottled* water have an expiration date?
gpt
The plastic bottle it is contained in does "expire," and will eventually start leaching chemicals into the water. This won't necessarily render the water toxic, but it might make it taste somewhat less than "mountain spring fresh." If consumers contact drink companies to complain that water they bought several years earlier tastes bad, the bottlers can point out that it's their own fault for not drinking it by the expiration date.