At 6 months old, your baby can start having 4 to 8 ounces of water per day. That’s roughly half a cup to one cup, and both the American Academy of Pediatrics and the CDC agree on this range. It’s a small amount for a reason: your baby still gets most of their hydration from breast milk or formula, and too much water can actually be dangerous at this age.
Why the Limit Is So Low
Breast milk is about 87% water. Formula, once mixed, is similarly water-dense. So your baby is already getting plenty of fluid from their regular feedings. The 4 to 8 ounces of water per day is meant to complement those feedings, not replace any of them.
The timing lines up with starting solid foods. As your baby begins eating purees or soft finger foods around 6 months, small sips of water help wash food down and get them used to drinking from a cup. Before 6 months, babies generally don’t need any water at all because breast milk or formula covers their entire fluid needs.
What Happens If a Baby Drinks Too Much Water
A baby’s kidneys are still developing and can’t process excess water as efficiently as an adult’s. When a baby takes in more water than their kidneys can excrete, the extra fluid dilutes the sodium in their blood, a condition called water intoxication. Sodium helps regulate fluid balance between cells, and when levels drop too low, water shifts into cells and causes swelling. The brain is the organ most vulnerable to this swelling.
Early signs of water intoxication include changes in behavior: your baby may seem unusually drowsy, irritable, or inattentive. More serious symptoms include nausea, vomiting, muscle twitching, poor coordination, irregular breathing, and in severe cases, seizures. This is rare when you’re sticking to the recommended range, but it’s the reason the ceiling exists. Don’t offer water freely throughout the day or use it as a way to stretch out feedings.
How to Offer Water at This Age
You don’t need to hit 8 ounces every day, especially when your baby is just starting out. A few sips at mealtimes is enough in the beginning. Offer water alongside solid foods rather than between milk feedings, so it doesn’t fill your baby’s stomach and crowd out the breast milk or formula they still depend on for calories and nutrients.
For the cup itself, start with a small open cup that you hold and tip for your baby. Open cups encourage better oral motor development than hard-spout sippy cups, which can interfere with the tongue movements needed for speech development later on. Once your baby can swallow a small amount of water from an open cup without too much spilling, you can also introduce a straw cup. Look for one that works with a normal sucking motion rather than requiring your baby to bite down on the straw. You can try both an open cup and a straw cup on the same day if your baby seems ready.
Expect mess. Your baby won’t be coordinated enough to hold or tilt a cup on their own yet, and a lot of water will dribble out. That’s completely normal and part of the learning process.
Hot Weather, Illness, and Dehydration
If your baby is sick with vomiting or diarrhea, or it’s especially hot outside, their fluid needs increase. In these situations, the priority is still breast milk or formula. Offer smaller, more frequent milk feedings first. You can give small sips of extra water on top of that, but the bulk of rehydration should come from their usual milk.
Signs of dehydration in a baby include a sunken soft spot on top of the head, sunken eyes, few or no tears when crying, fewer wet diapers than usual, and unusual drowsiness or irritability. If you notice these signs, increasing breast milk or formula intake is the first step. Persistent dehydration in a baby this young warrants medical attention.
Quick Reference: 6 to 12 Months
- Daily water range: 4 to 8 ounces (half a cup to one cup)
- When to offer: During meals with solid foods
- Best cup type: Open cup first, then straw cup
- Primary hydration source: Breast milk or formula, which should remain the main drink through the first year
- Before 6 months: No water needed
The amount stays at 4 to 8 ounces per day through 12 months. After your baby’s first birthday, water intake gradually increases as they transition away from formula or breast milk and eat a wider variety of solid foods.