Babies do not need juice. Babies younger than 6 months should not be given juice. However, if you choose to give your baby juice, do so only after 6 months of age, give only 100% fruit juice, and offer it only in a cup, not in a bottle. To help prevent tooth decay, do not put your child to bed with a bottle. If you do, make sure it contains only water.
Give your child extra water if he seems to be thirsty between feedings. During the hot months when your child is losing fluid through sweat, offer water 2 or more times a day. If you live in an area where the water is fluoridated, drinking water also will help prevent future tooth decay.
This was in addition to breastmilk, not as a replacement. I exclusively breastfeed my baby but wanted to see his facial expression with just a small amount off apple juice from Heinz suitable for 4+ months.