WHY does the expiration date on a bottle of drinking water refer to the bottle, not the water?

Drinking water itself has no expiration date - unlike the containers in which it is stored. When liquids are stored for long periods of time, plastic containers release chemicals that affect the taste and safety of the product. This does not mean that the water immediately becomes poisonous, but it gradually loses its freshness and can become stale.

It is believed that water in glass bottles retains its taste longer.