The pediatric community warns parents not to give water to babies younger than 6 months old. Why? Babies in this age range are still on an exclusive diet of breast milk or formula. Introducing water before this age could interfere with your baby’s ability to digest the milk she needs, and put her at risk for more serious health consequences. Even at 6 months old, babies should take no more than a few sips of water per day.
In the end, it can be prudent to wait until your baby’s first birthday or so before she starts drinking water regularly.
Whenever a baby’s digestion of breast milk or formula is disrupted, that baby misses out on nutrients that are essential for his or her growth and general health. Drinking water might also cause your baby to feel full, thereby cutting her appetite for milk.This is the most common risk of offering your child water too early. In rarer cases, giving a baby water too early can lead to water intoxication, though this would require larger amounts of water. Water intoxication dilutes the sodium in a baby’s body, leading to an electrolyte imbalance and swelling, puffy tissue, and can put babies at risk for seizures, brain damage, and even death.
Once your baby is officially eligible for her first H2O encounter, start her with just a few small sips of water from her bottle. As the weeks go by, you can slowly allow your baby more sips depending on how thirsty she is. By the time your baby’s 1-year birthday rolls around, you can stop the rationing and let her drink as much water as she wants.
If you plan to give your baby tap water, it's a good idea to check with your local water utility about water safety for infants and babies ahead of time. Water should not contain too much fluoride - for instance, no more than 0.7 mg per liter of water, since too much fluoride in her water and diet can lead to too much fluoride deposited on her teeth as they form beneath the gums. If your community's tap water has too much fluoride for your baby's growing teeth, you can buy a home water filter to filter excess fluoride out of the tap water, or you can buy low-fluoride water at the supermarket.
If you plan to use tap water, running the cold water in the faucet for about 3 minutes before drinking the water reduces the chances of lead and other mineral contamination. Using warm or hot water from the tap for drinking or cooking isn't recommended, because hot tap water contains a higher level of lead and other impurities.
If your local health department or your healthcare provider recommends boiling tap water before drinking it, bring the water to a high boil for a full minute before letting it cool. Extra boiling time is not recommended, as it can lead to a higher concentration of impurities as the water evaporates.
If you plan to use well water for your baby when she is less than a year old, make sure your well water has been tested for safety. Well water can contain an excess of nitrates, and boiling the water will only makes them more concentrated.