At our 5 week checkup my CHN recommended that I offer Aidyn some cooled boiled water for a couple of reasons. -
1. to help prevent constipation (which the formula can cause)
2. Because his appetite was SO excessive, and he was gaining so much, that she said to offer him the water every now and then just to quench his thirst, cause it was better than giving him extra bottles all of the time.

However all situations are different, so I would recommend having a chat to your GP or CHN about it like Kelly suggested.