Using water to clean water so you can add water

Right. AND the bottle itself gets dirty, inside and out and the mouth part.

The expiration date is for the bottle not the water.

According to science, the water in a bottle goes stale, not the bottle because it has air in the bottle with it. The CO2 in the air combines with the water to produce carbonic acid. Leaving hydroxyl ions in the water. This process makes the water more acidic and changes the flavor. Stale water, everyone.