Question: If water has been round for millions of years, why does it have a use by date on it?

Jason King answered on 13 Mar 2013:

Great question, and something I’ve always though strange too!
The main reason we have use by dates is because many foods will eventually have things like bacteria and mould growing in them which both makes them taste strange, and can potentially make us ill. Pure water however, has no nutrients in it at all for things to use as food. The only thing that might grow would be algae that may be able to use sunlight to give them energy, but if the bottle is unopened they wouldn’t be able to get in. In nature, water is constantly evaporating and falling as rain, which does quite a good job at keeping it clean, and tasting fresh.