It should be okay. It’s not that water is bad for any reason other than it has no nutritional value. And since their stomachs are so tiny, they need all the space for nutrients from formula/breastmilk and like for us as adults, water fills them up.
@Amalia it is actually bad to give a baby pure water as their kidneys are not mature enough to process it. I wouldn’t worry in this instance if baby seems well but shouldn’t make a habit of it. / remind husband of why it’s milk only at this stage.
It is not poisonous..just that their kidneys have not yet fully developed
It’s not ideal but it’s not poison. Should be ok :)