Babies can start drinking small amounts of water at 6 months old, when they begin eating solid foods. Before 6 months, breast milk or formula provides all the hydration an infant needs, and giving water earlier can be harmful.
Why Babies Under 6 Months Should Not Drink Water
A newborn’s kidneys are still immature and cannot efficiently process extra water. When a young baby takes in too much water, it dilutes the sodium in their blood, a condition called water intoxication. The CDC has documented cases where sodium levels dropped rapidly, causing cellular swelling in the brain and triggering seizures. Babies under 6 months are especially vulnerable because their kidneys can’t flush excess water the way an older child’s can.
There’s a second, quieter risk: water fills a baby’s tiny stomach without providing any calories or nutrients. Even small amounts can reduce how much breast milk or formula a baby drinks, which means fewer calories and less of the fat, protein, and vitamins they need to grow. Breast milk and formula are roughly 87% and 80% water respectively, so a baby who is feeding well is already getting plenty of fluid.
How Much Water From 6 to 12 Months
Once your baby starts solid foods around 6 months, you can offer water in a cup alongside meals. The CDC recommends 4 to 8 ounces per day for babies between 6 and 12 months. That’s roughly half a cup to one cup total, spread across the day. Think of it as a few sips with each meal rather than a full bottle.
At this stage, breast milk or formula is still your baby’s primary source of nutrition and hydration. Water is a complement, not a replacement. Offering it in an open cup or straw cup (rather than a bottle) also helps your baby practice drinking skills they’ll need as a toddler.
Water Intake After 12 Months
At one year, water becomes a regular part of your child’s diet. The recommended range jumps to 8 to 32 ounces per day (1 to 4 cups) for children 12 to 24 months old. By ages 2 through 5, that increases slightly to 8 to 40 ounces per day. The wide range reflects differences in body size, activity level, climate, and how much fluid your child gets from food and milk.
Whole milk typically enters the picture around 12 months as well, so your toddler’s daily fluid comes from a combination of water and milk rather than water alone.
What About Hot Weather or Constipation?
Parents often wonder whether a baby under 6 months needs water on a hot day. The answer is still no for most situations. Instead, offer more frequent breast or formula feedings. The extra fluid from those feedings is enough to keep a young baby hydrated, even in warm weather.
For constipation, the Mayo Clinic notes that babies 1 month and older can try a small amount of water or fruit juice (apple or pear juice works because it contains sorbitol, a natural compound that softens stool). This is a targeted, limited use, not routine daily water intake. If your baby is regularly constipated, the underlying feeding pattern is usually worth looking at rather than relying on water as a fix.
Tap Water, Bottled Water, and Fluoride
Fluoridated tap water is safe for preparing formula and for babies to drink once they’re old enough. One consideration: if your baby’s main food source is powdered or liquid concentrate formula mixed with fluoridated water, there’s a small chance of mild fluorosis, which shows up later as faint white lines on the teeth. It’s cosmetic, not harmful, but if it concerns you, alternating between fluoridated tap water and low-fluoride bottled water (labeled purified, demineralized, or distilled) can reduce exposure.
If you go the opposite direction and use only low-fluoride water, your baby’s doctor may recommend fluoride supplements starting at 6 months, since fluoride plays an important role in developing tooth enamel.
Signs of Too Much Water
Water intoxication is rare when parents follow age-appropriate guidelines, but it’s worth knowing the warning signs. When sodium levels drop too quickly, a baby may become unusually irritable or lethargic, develop a puffy or swollen face, or have a lower-than-normal body temperature. In severe cases, the sodium imbalance can cause seizures. If your baby has consumed a large amount of water and seems unusually drowsy, fussy, or unresponsive, that warrants immediate medical attention.
The simplest way to avoid this is to stick to the recommended amounts: no water before 6 months, 4 to 8 ounces a day from 6 to 12 months, and let breast milk or formula remain the main source of hydration throughout the first year.