Babies can start drinking small amounts of water at around 6 months old, when they begin eating solid foods. Before that age, breast milk or formula provides all the hydration an infant needs, and giving water too early can cause serious health problems.
Why 6 Months Is the Guideline
Both the American Academy of Pediatrics and the CDC recommend introducing water at about 6 months. The amount is small: 4 to 8 ounces per day, which is roughly half a cup to one cup. This isn’t really about hydration, since breast milk or formula still covers that. It’s more about letting your baby practice drinking from a cup and getting used to the taste of water.
If you live in an area with fluoridated tap water, those early sips also help protect developing teeth from future cavities.
Why Water Is Dangerous Before 6 Months
A young infant’s kidneys are too immature to handle extra water. When a baby under 6 months drinks water, the excess can dilute sodium levels in the blood, a condition called water intoxication. It doesn’t take much. A rapid drop in sodium causes cells in the brain to swell, which can lead to irritability, unusual sleepiness, low body temperature, swelling, and seizures.
Two factors make very young babies especially vulnerable. First, their kidneys can’t efficiently flush out extra water the way an older child’s or adult’s can. Second, babies have an intense hunger drive, so they may keep swallowing water even when their bodies don’t need it. The CDC has documented cases of seizures in infants who were given commercial bottled water as a supplement to formula.
This also means you shouldn’t water down formula to stretch it. Mixing formula with more water than the instructions call for has the same diluting effect on your baby’s blood sodium.
How Much Water From 6 to 12 Months
Between 6 and 12 months, stick to 4 to 8 ounces of water per day. Offer it in an open cup, sippy cup, or straw cup rather than a bottle. The goal at this stage is practice, not major fluid intake. Breast milk or formula remains the primary source of nutrition and hydration throughout the first year.
You don’t need to force it. Some babies take to water right away, while others show little interest for weeks. Either is normal. Offering small sips with meals or snacks is the easiest approach.
Water Intake After Age 1
Once your child turns 1 and transitions away from formula (or continues breastfeeding alongside regular food), water becomes a bigger part of daily hydration. Toddlers between 1 and 3 years old generally need about 4 cups of total fluids per day, with water and milk being the best options. Juice, if offered at all, should be limited to a small amount of 100% fruit juice.
At this age, keeping a cup of water accessible throughout the day helps your child learn to drink when thirsty. Most toddlers self-regulate their fluid intake fairly well as long as water is available.
Tap Water, Bottled Water, and Fluoride
Fluoridated tap water is generally fine for babies 6 months and older and offers the added benefit of supporting dental health. For babies under 6 months, it’s safe to use fluoridated tap water to mix formula, though there is a small risk of mild dental fluorosis, which causes faint white spots on teeth. If that concerns you, you can use bottled or purified water without fluoride, or choose ready-to-feed formula that doesn’t require mixing.
Most cases of fluorosis from formula preparation are cosmetically mild and don’t affect tooth function.
The Exception: Constipation in Young Babies
There is one situation where a small amount of water may be appropriate before 6 months. The Mayo Clinic notes that for babies 1 month and older who are constipated, a small amount of water can help soften stools. Water is usually the first thing to try before fruit juice. “Small amount” here means an ounce or two, not a full bottle. If your baby is regularly constipated, it’s worth bringing up at your next pediatric visit rather than routinely supplementing with water on your own.