Babies under 6 months old should not drink any water at all. From 6 to 12 months, babies can have 4 to 8 ounces of water per day, which is roughly half a cup to one cup. These limits exist because a baby’s kidneys are too immature to process extra water safely, and breast milk or formula already provides all the hydration they need.
Why No Water Before 6 Months
Breast milk and formula are about 80 to 90 percent water, so even on hot days, a young baby gets plenty of fluids from regular feedings. Adding water on top of that creates two problems. First, it fills up a tiny stomach, which means the baby takes in fewer calories and nutrients from milk. Second, and more seriously, a young infant’s kidneys can’t efficiently clear excess water from the body. When too much water enters the bloodstream, it dilutes sodium levels and causes cells to swell, particularly in the brain. This condition, called water intoxication, can trigger seizures in infants when sodium drops rapidly.
Several factors make babies under 6 months especially vulnerable. Their kidneys are still developing, so they can’t shed extra fluid the way an older child or adult can. They also have a powerful hunger drive that can lead them to gulp down whatever liquid is offered, whether it’s milk or water. Even small amounts of unnecessary water can throw off the delicate electrolyte balance in a body that weighs only 8 to 15 pounds.
What About Hot Weather or Illness?
Parents often worry their baby needs extra water during a heat wave or when running a fever. The American Academy of Pediatrics is clear on this: on hot days, breastfed infants should be offered additional breast milk, not water. Formula-fed babies can be given extra formula. The answer for the first 6 months is always more milk or formula, never plain water. If your baby seems unusually thirsty, offering more frequent feedings is the safe approach.
Water From 6 to 12 Months
Once babies start eating solid foods around 6 months, you can introduce small amounts of water. Both the CDC and the AAP recommend 4 to 8 ounces per day during this stage. That’s a modest amount, roughly a few sips at each meal, because breast milk or formula still provides the vast majority of a baby’s hydration and nutrition through the first year.
This is also a good time to introduce an open cup. Putting just a small splash of water in a cup and helping guide it to your baby’s mouth lets them practice the sipping and swallowing motions that build coordination. You don’t need to worry about hitting a specific daily target. A few sips with meals is fine. The goal is gentle practice rather than major hydration.
After the First Birthday
Once your child turns one, water becomes a bigger part of daily hydration. Toddlers between 1 and 2 years old generally need about 1 to 4 cups of water per day, depending on their size, activity level, and how much milk they’re drinking. At this stage, whole milk (up to about 16 ounces daily) and water should be the primary beverages. Juice, flavored milk, and sugary drinks aren’t necessary and can displace the nutrients toddlers need.
Risks of Too Much Water
Water intoxication is rare, but it happens most often in infants. When excess water floods a baby’s system faster than their kidneys can handle it, sodium in the blood drops sharply. Early signs include irritability, drowsiness, and a bloated stomach. A baby might also seem unusually sleepy or have muscle weakness. If sodium continues to fall, symptoms can progress to seizures, loss of consciousness, and in extreme cases, coma.
One overlooked risk is over-diluting formula. Some parents stretch formula by adding extra water, either to save money or because they believe the mixture is too concentrated. This effectively gives the baby excess water with every feeding while cutting the calorie and nutrient content. Over time, this leads to poor growth and the same electrolyte imbalances seen in water intoxication. Formula should always be mixed exactly as the label directs.
Quick Reference by Age
- 0 to 6 months: No water. Breast milk or formula only.
- 6 to 12 months: 4 to 8 ounces of water per day, offered in small sips alongside solid foods.
- 12 to 24 months: 1 to 4 cups of water daily, alongside whole milk.
If your baby ever shows signs of unusual drowsiness, swelling, or irritability after drinking water, or if you suspect they’ve consumed a large amount, contact your pediatrician or go to an emergency room. These symptoms can escalate quickly in a small body.