Babies can start having small amounts of water at 6 months old, when they begin eating solid foods. Before that age, breast milk or formula provides all the hydration an infant needs, even in hot weather. From 6 to 12 months, the recommended amount is 4 to 8 ounces per day, which is roughly half a cup to one cup.
Why Babies Under 6 Months Shouldn’t Drink Water
An infant’s kidneys are not mature enough to handle extra water in the first months of life. When a young baby takes in too much water, it dilutes the sodium in their blood. This condition, called water intoxication, happens when sodium levels drop below a critical threshold and the resulting fluid imbalance causes cells in the brain to swell. The CDC has documented cases of seizures in infants who were given commercial bottled water as a supplement.
Two factors make babies under 6 months especially vulnerable. First, their kidneys can’t efficiently flush excess water the way an older child’s can. Second, young infants have a powerful hunger drive that can lead them to consume large volumes of liquid quickly, making it easy to overshoot what their small bodies can process. Even a few extra ounces can push total body water up by 7% to 8%, enough to trigger symptoms.
This rule holds even during summer heat. Breastfeeding parents should increase their own water intake so their milk supply stays strong, and formula-fed babies can be offered more frequent feedings. Neither group needs supplemental water before 6 months.
How Much Water From 6 to 12 Months
Once your baby starts solids around 6 months, you can introduce water at 4 to 8 ounces per day. This isn’t meant to replace breast milk or formula, which should still be the primary source of nutrition and hydration throughout the first year. Think of water as a complement to meals, not a stand-alone drink.
You don’t need to hit a specific target. Some babies take a few sips and lose interest, which is perfectly fine. The goal is to let them get used to the taste and practice drinking, not to meet a quota. Offering water alongside solid foods at mealtimes is the simplest approach.
Best Cup for a Baby’s First Sips
An open cup is the best choice for introducing water. It teaches babies to form their lips around the rim and sip rather than suck, which supports healthy oral development. A small, two-handled training cup with a weighted base can help reduce spills while your baby learns.
If you need a lid to contain the mess, choose one that snaps or screws on without a valve. Spill-proof cups, including 360-degree rim cups and valve-based sippy cups, encourage a sucking motion that doesn’t teach babies how to regulate their intake. A straw cup is another good option, as it also promotes sipping. The key is moving away from the same sucking pattern your baby uses with a bottle or breast.
Signs of Water Intoxication
Water intoxication is rare when parents follow the guidelines above, but it’s worth knowing what to watch for. Early signs include nausea or vomiting, a bloated belly, unusual drowsiness, and irritability. You might also notice muscle weakness or swelling in the hands, feet, or abdomen. In severe cases, symptoms can progress to seizures, confusion, or loss of consciousness. If your baby seems unusually lethargic or unresponsive after consuming water, that warrants immediate medical attention.
Fluoride and Water Safety
If you mix powdered or liquid-concentrate formula with tap water, fluoride is worth considering. Fluoridated water is safe for most people, but when formula mixed with fluoridated water is a baby’s primary food source, it can slightly increase the chance of mild dental fluorosis, which causes faint white spots on the teeth later in childhood.
You can reduce this risk by alternating between tap water and low-fluoride bottled water for some feedings. Look for bottles labeled “purified,” “distilled,” “deionized,” or “demineralized,” as these contain little to no fluoride unless it’s listed as an added ingredient. Some bottled water brands are specifically marketed for mixing with infant formula. If you’re offering sips of water to a baby over 6 months, the small volume involved (a few ounces a day) makes fluoride exposure minimal.
Water After the First Birthday
Once your child turns 1, water becomes a more central part of their diet. Most toddlers transition from breast milk or formula to whole milk and water as their main beverages. At this stage, you can offer water freely throughout the day alongside meals and snacks. Letting your toddler drink when thirsty, rather than pushing a set amount, helps them learn to recognize their own hydration cues. Juice, flavored milks, and sweetened drinks are best avoided or limited, as water and plain milk cover a toddler’s hydration needs without added sugar.