Babies can start drinking small amounts of water at 6 months old, when they begin eating solid foods. Before 6 months, breast milk or formula provides all the hydration an infant needs, and giving water earlier can be genuinely dangerous. The CDC recommends 4 to 8 ounces of water per day for babies between 6 and 12 months.
Why Babies Under 6 Months Shouldn’t Have Water
A newborn’s kidneys are not mature enough to handle plain water properly. Although kidney formation is complete before birth, the internal structures that concentrate urine and manage water balance continue developing during the first year of life. Specifically, a young infant’s kidneys can’t efficiently reabsorb water the way an older child’s or adult’s kidneys can. This means even a modest amount of extra water can throw off the delicate balance of sodium and other electrolytes in a baby’s blood.
Breast milk and formula are carefully balanced to match what an immature kidney can process. They deliver hydration alongside the right concentration of nutrients and electrolytes. Plain water, on the other hand, is “solute-free,” meaning it dilutes a baby’s blood without adding anything to maintain that balance. Even on hot days, healthy babies under 6 months get all the water they need from their regular feedings.
The Risk of Water Intoxication
Water intoxication sounds extreme, but it’s a real and documented risk in young infants. It happens when too much plain water dilutes the sodium in a baby’s bloodstream, a condition called hyponatremia. Symptoms begin when sodium levels drop sharply and total body water increases by roughly 7% to 8% or more. At that point, cells in the brain begin to swell, which can cause irritability, unusual sleepiness, low body temperature, swelling, and seizures.
Babies under 6 months are especially vulnerable for two reasons: their kidneys can’t efficiently clear excess water, and their strong hunger drive means they may readily accept a bottle of water even when they don’t need it. The combination makes it easy for a well-meaning parent to accidentally overload a small body with fluid it can’t process. This is also why you should never water down formula to stretch it. Always follow the mixing instructions on the container.
How Much Water at 6 to 12 Months
Once your baby starts solids around 6 months, you can introduce water in small amounts. The recommended range is 4 to 8 ounces per day, which is roughly half a cup to one cup. Think of it as sips throughout the day, not a full bottle at once. A small open cup or a straw cup with meals is a common way to offer it.
At this stage, breast milk or formula is still the primary source of nutrition and hydration. Water is more of a complement, helping your baby get used to the taste and practice drinking from a cup. You don’t need to stress about hitting a specific ounce target every day. Some babies take to water quickly, others show little interest, and both are normal.
After the First Birthday
Once your child turns 1, water becomes a much bigger part of their daily routine. Most toddlers transition away from formula entirely, and breast milk often decreases as solid food intake grows. Water and whole milk become the main beverages. There’s no need to limit water to a few ounces at this point. You can offer it freely with meals and snacks, letting your child drink when thirsty.
By around 12 months, kidney function has matured significantly, reaching closer to adult levels of water-processing ability. The risk of water intoxication drops considerably because the body can now regulate fluid balance much more effectively.
Tap Water, Bottled Water, and Fluoride
For most families, regular tap water is perfectly safe for babies 6 months and older. You don’t need to boil or filter it unless your local water supply has known contamination issues. The CDC does recommend extra precautions for babies under 2 months, premature infants, or those with weakened immune systems. For those babies, boiling the water and letting it cool for about five minutes before use helps kill bacteria that can survive in powdered formula.
If your tap water is fluoridated, that’s generally fine. The risk of dental fluorosis (faint white spots on adult teeth) from fluoridated water mixed with formula is considered low. The most critical period for fluorosis occurs later in childhood, when most kids have already moved past formula. If you’d rather minimize fluoride exposure, you can use water labeled as purified, distilled, or reverse osmosis filtered. But this is a precautionary choice, not a medical necessity for most families.
If you ever suspect your tap water is contaminated with chemicals or toxins, boiling won’t help. In that situation, use bottled water and follow any guidance from local public health authorities.
Practical Tips for Introducing Water
- Start small. Offer a few sips from an open cup or straw cup at mealtimes. There’s no need for a full bottle of water.
- Don’t replace feedings. Water should never take the place of a breast milk or formula feeding between 6 and 12 months. Those feedings are still delivering the calories and nutrients your baby depends on.
- Skip juice and flavored water. Plain water is the best option. Juice adds sugar without nutritional benefit at this age.
- Watch for hot weather. On very warm days, you can offer water a bit more frequently, but breast milk and formula still do the heavy lifting for hydration.
- Don’t force it. If your 7-month-old pushes the cup away, that’s okay. They’re likely getting enough fluid from milk and the moisture in solid foods. Try again at the next meal.