evidence: But children under a year old don’t need water like adults do. It can actually be dangerous for them. Babies get all their hydration from breast milk or formula. [...] A baby should drink only breast milk or formula until they’re six months old. It has all the hydration and nutrition they need in the early months. [...] When babies are between 6 and 12 months of age, breast milk or formula continues to be a priority over water. But if you offer breast milk or formula first, you can then offer water, 2-3 ounces at a time. At this age, 4-8 ounces a day of water is enough. More than that may lead to water intoxication.