While you are supposed to mix milk powder formula (powdered formula) with water, you shouldn’t give a baby under six months any water at all otherwise. Infants get all of the nutrients and liquids they need from breast milk or formula. You can start introducing water when your baby begins eating solid foods. Your baby has a very small belly that fills up quickly. You should be cautious of the amount of water you give because it could take up valuable space for other nutrients your child needs to thrive and be healthy.