Remember that according to the American Academy of Pediatrics, "During the first 6 months of age, even in hot climates, water and juice are unnecessary for breastfed infants." And there is no good reason to think that the advice would be any different for a baby who is drinking formula instead of nursing.
Water or Juice for Constipation
Is there ever a good reason to give your baby water or juice before he is six months old?Constipation is the main condition that might lead you to give your baby a few ounces of water or juice each day to help soften his bowel movements. Keep in mind that babies who are exclusively breastfed very rarely get constipated though. So even if your breastfed baby is only having bowel movements every few days or once a week, which is common by two or three months of age, then he likely isn't constipated if he is feeding well and eventually has a soft bowel movement.
Formula-fed babies can become constipated though. So from time to time, your pediatrician might advise a few ounces of water or juice a day for your baby. If this becomes a routine problem, a change from a milk-based formula to a soy formula might be helpful since chronic constipation can be a sign of a formula intolerance.
Source: American Academy of Pediatrics Policy Statement. Breastfeeding and the Use of Human Milk. Pediatrics 2005 115: 496-506.
