Babies can start drinking small amounts of water at around 6 months old, when they begin eating solid foods. Before that age, breast milk or formula provides all the hydration an infant needs. Between 6 and 12 months, the recommended amount is 4 to 8 ounces per day, roughly half a cup to one cup.
Why Babies Under 6 Months Shouldn’t Have Water
A newborn’s kidneys are physically immature and can’t process plain water the way an older child’s can. The system that concentrates urine and regulates water balance develops over the first several months of life. In young infants, the kidneys respond poorly to the hormone that tells them to hold onto or release water. On top of that, the inner part of the kidney lacks the concentration of salts and other molecules it needs to properly filter excess fluid. The result is that even a small amount of extra water can overwhelm a young baby’s system.
When an infant takes in too much water, sodium levels in the blood can drop dangerously low. This condition, called water intoxication, causes irritability or unusual sleepiness, low body temperature, swelling, and in severe 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 only a few pounds. This is why pediatric guidelines are firm: no plain water before 6 months.
There’s a nutritional concern too. A baby’s stomach is tiny, and water fills it without providing any calories or nutrients. Giving water to a young infant can displace breast milk or formula, which are the sole sources of nutrition during those first months.
How Much Water From 6 to 12 Months
Once your baby starts solids around 6 months, you can offer 4 to 8 ounces of water per day. This isn’t meant to replace breast milk or formula. It’s a small supplement that helps your baby get comfortable with water and practice drinking from a cup. Most of their hydration still comes from milk feeds during this stage.
You don’t need to stress about hitting a specific ounce count. A few sips with meals is a reasonable starting point. The goal is familiarity, not a quota. Some babies take to water right away, while others show little interest for weeks. Both are normal.
Choosing the Right Cup
Six months is also a good time to introduce cup drinking. Small open cups, like medicine cups, work surprisingly well because they help babies learn the coordination of sipping rather than sucking. Open training cups with two handles are another option. Sippy cups and straw cups are fine for on-the-go situations where spills are a concern, but practicing with an open cup early builds better drinking skills over time.
Expect mess. Learning to drink from a cup takes patience and repetition. Holding the cup for your baby and tipping it gently lets them get used to the sensation of water in their mouth. Over several weeks, most babies start reaching for the cup and attempting to hold it themselves.
After the First Birthday
Water intake naturally increases once your child turns one and starts eating a wider variety of solid foods. At this point, water and milk become the primary drinks. Juice, flavored waters, and sugary drinks aren’t necessary and can crowd out more nutritious options. Offering water throughout the day, especially with meals and snacks, helps establish a healthy habit early.
Signs Your Baby Is Well Hydrated
The simplest way to check hydration is diaper output. After the first week of life, a well-hydrated baby produces at least six wet diapers per day, with no more than about eight hours between wet diapers. This holds true whether your baby is getting hydration from milk alone or from milk plus small amounts of water.
Signs of dehydration to watch for include dry or cracked lips, no tears when crying, unusual sleepiness or fussiness, fast breathing or heart rate, cold or dry skin, and a sunken soft spot on top of the head. If you notice several of these together, your baby needs medical attention promptly.