Hi
I would say the only time you really need to give a bottle feed baby water is if there's a possibility of them becoming dehydrate - i.e if they're ill and aren't taking bottles, if they've taken bottles but consistently puked them back up, if it's particularly hot or if you're trying to wean them from habitual night wakjng when you've been giving formula but they aren't really hungry.
Other than that there should be sufficient water in their bottles to keep then hydrated.
love
