It's not a good idea to give your baby water until they are about 6 months old. Babies get all the hydration they need from breast milk or formula.
Giving a baby younger than 6 months old too much water can interfere with their body's ability to absorb the nutrients in breast milk or formula. It can also cause his tummy to feel full, which curbs his desire to feed.
Giving your baby small amounts of water before it's 6 months old probably won't harm them, but it's best to check with your doctor first.
While water may be okay for formula fed babies when it's hot outside or when they have a fever, it is not necessary or good for breastfed babies. Breast milk is 88% water. Babies get all the water and nutrients they need from breast milk, and any other supplement will just get in the way of that. If it's hot out, increase nursing frequency. For instance, breastfeed once an hour instead of every 2-3 during the day.
To go along with what Angelee said, the only exception as to giving your child water younger than 6 months is in the summer time if your outside in the heat. Even then though, the child shouldnt drink more than one ounce of water to keep hydrated.
They can have boiled and cooled water from birth but only best when they have had a good bottle/breast feed.The health visitor advised i gave my daughter water after her feed cos she got thirsty but never before her feed.