evidence: But adults and babies have very different dietary needs. Newborns and babies up to 6 months old should never drink water. [...] Once your baby is six months old, it’s okay for them to have some water. But it’s important to limit how much water they drink. [...] These recommendations are for total daily intake, not for intake at one sitting. Start by giving 6-month-old babies 2 ounces of water at a sitting.