Is there any good reason why we shouldn’t refill our water bottles?

The long-running series in which readers answer other readers’ questions on subjects ranging from trivial flights of fancy to profound scientific conceptsThe water bottle I refill and drink out of most days at work has a blurb on the back stating, “Once opened, keep refrigerated and consume within 3 days. Serve chilled. FOR HYGIENE REASONS REFILLING IS NOT RECOMMENDED” (their emphasis). Is there any plausible reason for this? It is only water – why on earth does it need t