Babies can start drinking 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. Between 6 and 12 months, the CDC recommends offering 4 to 8 ounces of water per day.
Why Babies Under 6 Months Shouldn’t Have Water
A newborn’s kidneys are roughly the size of a grape, compared to adult kidneys that are closer to the size of an avocado. That dramatic size difference means infant kidneys simply can’t filter out excess fluid the way yours can. When a young baby takes in plain water, it can dilute the sodium in their bloodstream, creating a dangerous condition called hyponatremia (sometimes called water intoxication). Symptoms include irritability, drowsiness, and in severe cases, seizures.
Water also fills up a baby’s tiny stomach without delivering any calories or nutrients. Every ounce of water an infant drinks is an ounce of breast milk or formula they’re not drinking, which means fewer of the fats, proteins, and vitamins they need for rapid growth. This is especially risky in the first months of life, when weight gain is a key marker of healthy development.
What About Hot Weather or Illness?
Even during summer heat, healthy newborns get all the water they need from breast milk and formula. The instinct to offer a little extra water on a hot day makes sense for older kids and adults, but it doesn’t apply to babies under 6 months. If you’re concerned your infant is overheating, more frequent breast milk or formula feedings are the safer way to keep them hydrated.
How Much Water at 6 to 12 Months
Once your baby starts solid foods around 6 months, you can introduce water in small amounts. The guideline is 4 to 8 ounces per day, which works out to roughly half a cup to one cup total. You don’t need to offer it all at once. A few sips with meals or between feedings is plenty. Breast milk or formula should still be the primary source of nutrition and hydration throughout the first year.
Think of water at this stage as practice rather than a major fluid source. Your baby is learning a new skill (drinking something other than milk) and getting familiar with the taste. There’s no need to push a certain amount. If your baby only takes a sip or two, that’s fine.
Choosing the Right Cup
Six months is also a good time to start practicing with a cup. Open cups are worth trying early because they help babies develop the lip and tongue coordination they’ll need later. A small, non-breakable open training cup with two handles is easy for little hands to grip. You can also try sippy cups, straw cups, or small medicine cups to see what your baby prefers.
Start with just a tiny amount of liquid in the cup. Let your baby play with it first to get used to how it feels before you help guide it to their mouth. Tipping the cup gently so they feel the water on their lips helps them understand what to do. Using a cup yourself at mealtimes is one of the most effective teaching tools, since babies at this age love to imitate.
Tap Water, Filtered Water, or Bottled Water
Fluoridated tap water is generally safe for infants. The CDC and state health departments have concluded that water fluoridated at standard levels poses no known health risks for babies. However, if you’re concerned about a cosmetic condition called enamel fluorosis (faint white spots that can appear on developing teeth), you can use water labeled as purified, distilled, deionized, or reverse osmosis filtered. The actual risk of fluorosis from tap water mixed with formula is considered low, but the option is there if it matters to you.
If your home uses well water or you’re unsure about your local water quality, having it tested is a reasonable step. For babies between 6 and 12 months, cooled boiled tap water is a safe default.
After 12 Months
Once your baby turns one, water becomes a regular part of their daily diet. At this point, their kidneys are mature enough to handle larger volumes, and they’re transitioning away from formula (or continuing to breastfeed alongside a full diet of solid foods). You can offer water freely throughout the day, especially with meals and snacks. Whole milk typically replaces formula around this age, and water fills in the gaps between meals to keep your toddler hydrated.