evidence: Water is not recommended for your baby in his first six months. Until your little one is eating solid food, your baby will get all the water he needs from breast milk (which is actually 80 percent water) or formula. After your baby turns 6 months old, you can start offering a little water. Why Shouldn’t You Give Water to Your Baby Under 6 Months? For babies under 6 months, drinking water can lead to diarrhea and even malnutrition.