At 6 months old, your baby can have 4 to 8 ounces of water per day, which is about half a cup to one cup. This small amount is meant to complement breast milk or formula, not replace it. Water becomes appropriate once your baby starts eating solid foods, typically around the 6-month mark.
Why the Limit Is So Low
A baby’s kidneys are not fully developed at 6 months. The structures responsible for concentrating urine and managing fluid balance continue maturing through the first year of life, only reaching adult-level function around 12 months. Until then, an infant’s kidneys struggle to process large volumes of water efficiently. They can’t flush out excess water the way an older child or adult can, which means even moderate amounts of extra water can dilute the sodium in their blood to dangerous levels.
Before 6 months, healthy babies don’t need any water at all. Breast milk and formula already provide all the hydration an infant needs for growth and to replace fluid lost through breathing, sweating, and diaper output. The shift at 6 months isn’t because babies suddenly need more hydration. It’s because they’re starting solid foods, and small sips of water help them learn to drink from a cup and can ease digestion of new textures.
How to Offer Water Practically
The American Academy of Pediatrics recommends offering water in an open cup, sippy cup, or straw cup starting around 6 months. You don’t need to measure out exact portions at each meal. A few sips with solid food, a few more throughout the day, totaling somewhere in the 4 to 8 ounce range, is the goal. Most babies at this age won’t drink much at a time anyway.
Think of water as a companion to meals rather than something your baby needs between feedings. If your baby takes a few sips and pushes the cup away, that’s fine. Breast milk or formula remains the primary source of both nutrition and hydration through the entire first year. Water is supplemental, not a replacement.
The Risk of Too Much Water
Water intoxication is rare but serious in infants. It happens when excess water dilutes sodium in the blood, a condition called hyponatremia. Sodium levels drop rapidly, and the brain responds poorly. Early symptoms include nausea, vomiting, bloating, drowsiness, and irritability. If it progresses, it can cause seizures, loss of consciousness, and in extreme cases, death.
Symptoms can develop when total body water increases by as little as 7 to 8 percent. For a baby weighing around 16 pounds, that’s a surprisingly small volume. Infants under 6 months are at highest risk because of their immature kidneys and smaller body size, but 6-month-olds are still vulnerable if given water freely throughout the day or if water replaces milk feedings.
One common scenario flagged by the CDC involves parents diluting formula with extra water to stretch supplies, or offering bottles of water to soothe a fussy baby. Both can push fluid intake past safe levels without parents realizing it.
Water Can Crowd Out Essential Nutrition
Beyond the risk of water intoxication, there’s a simpler concern: water fills your baby’s stomach without providing any calories, fat, protein, or vitamins. At 6 months, babies are growing rapidly and depend on breast milk or formula for the vast majority of their nutritional needs. If water takes the place of even one or two milk feedings per day, your baby may not get enough calories to support healthy weight gain and development.
This is why the recommendation stays at 4 to 8 ounces. It’s enough for your baby to practice drinking and to wash down solid food, but not enough to interfere with appetite for milk.
Hot Weather and Illness
Parents often wonder whether babies need extra water during summer heat or when they’re sick. In hot weather, the CDC recommends making sure infants drink plenty of fluids, but for a 6-month-old, that primarily means more frequent breastfeeding or formula feeds rather than large increases in water. You can offer water a bit more freely on very hot days, but staying within or close to the 4 to 8 ounce range and increasing milk feeds is the safer approach.
During illness, especially with vomiting or diarrhea, fluid loss is a real concern. However, plain water is not the best replacement because it lacks the sodium and electrolytes your baby is losing. Extra breastfeeding is the first line of defense, and if your baby is showing signs of dehydration (fewer wet diapers, dry mouth, no tears when crying), your pediatrician may recommend an oral rehydration solution rather than plain water.
What Changes After 12 Months
Once your baby turns one, their kidneys have matured enough to handle larger volumes of water, and they’re transitioning away from formula or breast milk as their primary drink. At that point, the recommended water intake increases to around 1 to 4 cups per day alongside whole milk. Until then, treat water as a small addition to your baby’s diet: a few ounces a day in a cup at mealtimes, with breast milk or formula still doing the heavy lifting.