A 6-month-old can safely drink 4 to 8 ounces of water per day, according to the CDC. That’s roughly half a cup to one cup total across the entire day, not per sitting. Before 6 months, babies should not have water at all.
Why the Limit Is So Low
Eight ounces might sound like almost nothing, but a 6-month-old’s kidneys are still maturing and can’t process large volumes of water the way an adult’s can. When an infant takes in too much water, sodium levels in the blood drop rapidly. This condition, called water intoxication, causes irritability, drowsiness, low body temperature, swelling, and in serious cases, seizures. It happens when total body water increases by roughly 7 to 8 percent or more, which doesn’t take much in a baby who weighs 15 or 16 pounds.
Infants under 6 months are at even higher risk because their kidneys are less developed and their hunger drive is so strong they’ll drink whatever is offered. That’s why both the CDC and the World Health Organization recommend no water at all before 6 months, not even in hot weather. Breast milk and formula already contain all the water a young baby needs.
Water Can Crowd Out Calories
Even within the safe range, water fills a baby’s tiny stomach and creates a feeling of fullness. If your baby drinks water before or during a feeding, they may take in less breast milk or formula as a result. That matters because milk is still providing the vast majority of their calories and nutrients at 6 months. Replacing milk volume with water can lead to insufficient calorie intake, slower weight gain, and reduced intake of the immune-supporting compounds found in breast milk.
Think of water at this age as a complement to meals, not a drink your baby needs to stay hydrated. Their milk intake is handling hydration. The water is mainly there to introduce the taste and the skill of drinking from a cup.
How to Offer Water at 6 Months
The best time to offer a small amount of water is alongside solid foods, which most babies start around 6 months. A few sips with a meal is plenty. You don’t need to track ounces precisely or stress about hitting the full 8 ounces. Most babies at 6 months will only take a few sips anyway.
This is also a great time to introduce an open cup. Small, non-breakable cups with two handles are easiest for babies to grip. Start by putting just a tiny amount of water in the cup, then help guide it to your baby’s mouth. Tip the cup gently so they can feel the liquid on their lips. Expect mess. The goal is practice, not volume. Using a cup yourself during meals helps too, since babies at this age love to imitate what they see.
Sippy cups and straw cups work well for preventing spills, but practicing with an open cup early builds better drinking skills over time. You can alternate between the two depending on the situation.
Hot Weather and Illness
Parents often wonder whether babies need extra water on hot days. For healthy infants who are still getting regular breast milk or formula, the answer is generally no. Their milk already adjusts to meet hydration needs. If your baby seems thirstier in the heat, offering more frequent milk feedings is a better approach than adding extra water beyond the 4 to 8 ounce guideline.
During illness, especially if your baby has vomiting or diarrhea, fluid replacement becomes more important, but water alone isn’t the right solution. Milk feedings and, if recommended by your pediatrician, an oral rehydration solution are more effective because they replace both fluids and the electrolytes a baby is losing.
What Changes After 12 Months
Once your baby turns 1, their kidneys are more developed and they’re eating a wider variety of solid foods. Water intake naturally increases at that point, and the strict limits loosen. Most toddlers between 12 and 24 months do well with around 1 to 4 cups of water per day, depending on how much milk they’re still drinking and how active they are. The transition happens gradually as solids become a bigger part of their diet and milk feedings taper off.