No need for additional water in the first six months of life
We ask that you not give water to your baby in the first six months of life for several reasons
All the water the baby needs is in the breast milk the baby is being exclusively fed with. For formula-fed babies, all the water they need is in the formula. In breastfed babies, almost 80% of the foremilk is water
The newborn and infant tummy are quite small: the stomach can hold no more than 5 to 10 ml of fluid at birth. This is why we say even though your breast milk seems so little, feed them with it, that is all they can reasonably take anyway.
Babies need calories AND fluid- breast milk provides both, water only provides fluid, and on its own takes up much-needed space for brain calories that milk contains ( small stomach, remember)
The more serious reason not to give water at this age is that they can develop water intoxication: when the kidneys have too much water to handle
Babies can develop water intoxication with as little as one ounce - 30 ml of water- which can dilute the salt in the baby’s bloodstream to the extent that the very small sized and underdeveloped kidneys fail to process it properly, salt levels drop in the blood and this causes baby’s brain to swell- a terrible situation for baby, their parents and for their doctors.
This is also a reason not to overdilute a baby’s formula.
After the age of six months, you should still limit the amount of water you give- why give water when you can give calorie-rich breast milk