In this heat parents often wonder if their newborn is thirsty, and some will offer water, or add extra water when mixing formula, DON'T!! As adults we are constantly reminded that drinking water is good for us to stay hydrated, but for a newborn, it's a completely different story. A baby will receive all the fluids they need from breastmilk or formula, and there is no need for any additional water. Offering a newborn water could not only interfere with their daily nutritional needs, as they may become too full to drink milk, but it is actually potentially dangerous too.
Simply, a newborn's kidneys are immature and giving a baby too much water can upset the electrolyte balance causing a condition called Water Intoxication. Water intoxication happens when too much water dilutes the concentration of sodium in the body, and causes tissues to swell. Generally it is the brain that is affected. Symptoms include irritability, drowsiness and other mood changes. Other symptoms are low temperature, puffiness and swelling in the face, seizures, and even a coma.
Once baby is 6 months old, it is generally considered safe to offer a few sips, here and there, but always check with your pediatrician first.