A 10-month-old can safely drink 4 to 8 ounces of water per day, which is about half a cup to one cup. That range comes from both the CDC and the American Academy of Pediatrics, and it applies to all babies between 6 and 12 months of age. At this stage, water is a supplement to your baby’s diet, not a primary source of hydration. Breast milk or formula still handles most of that job.
Why the Limit Is So Low
Four to eight ounces sounds like almost nothing, and that’s intentional. Your baby’s kidneys are still maturing and can’t flush out large volumes of water the way an adult’s can. When an infant takes in too much plain water, the extra fluid dilutes sodium levels in the blood. If sodium drops quickly enough, it causes cells in the brain to swell, which can lead to seizures, confusion, or worse. This condition, called water intoxication, is rare but serious, and infants are uniquely vulnerable to it because of their small body size and still-developing kidneys.
There’s a second, more common concern: water fills a baby’s stomach without providing any calories, fat, or nutrients. A 10-month-old’s stomach is small, and every ounce of water that goes in is an ounce of breast milk or formula that doesn’t. Over time, too much water can displace the calories your baby needs to grow. Breast milk or first infant formula should remain the main drink through the entire first year.
How Water Fits Into a 10-Month-Old’s Day
By 10 months, most babies are eating solid foods at two or three meals a day. Water works best offered in small sips alongside those meals, not as a standalone drink between feedings. Think of it as practice for the cup and a way to help wash down food rather than a hydration strategy. Your baby is still getting the bulk of their fluids from breast milk or formula, which is mostly water already.
If your baby is on formula, a rough guideline from the NHS is about 400 milliliters (around 13.5 ounces) of formula per day at this age, though individual needs vary. That formula, combined with the water content in solid foods like fruits and vegetables, covers most of your baby’s hydration needs. The extra 4 to 8 ounces of plain water is just a small addition on top of that.
Hot Weather and Illness
Parents often wonder whether to increase water during a heat wave or when their baby has a fever. The CDC recommends keeping young children cool and hydrated in hot weather, but for babies under 12 months, extra breast milk or formula feedings are generally the better approach. These provide fluids along with electrolytes and calories, while plain water does not. If your baby seems thirstier than usual during a hot stretch, offering a few extra sips of water at meals is reasonable, but additional milk or formula feedings are more effective for true rehydration.
Signs a Baby Has Had Too Much Water
Sticking to the 4 to 8 ounce guideline makes water intoxication extremely unlikely. But it’s worth knowing what to watch for, especially if another caregiver might offer more water than expected. Early signs include unusual fussiness, drowsiness, a bloated-looking belly, or nausea and vomiting. In more severe cases, you might see muscle weakness, swelling in the hands or feet, or a sudden change in alertness. Seizures are a late and dangerous sign. If your baby seems unusually lethargic or unresponsive after drinking a large amount of water, that warrants immediate medical attention.
Choosing the Right Cup
Ten months is a great time to build cup skills. Your baby can likely sit independently, hold objects with both hands, and bring things to their mouth, all signs they’re ready. An open cup with no lid is actually the best option for development. It teaches your baby to sip rather than suck, which supports healthy oral and speech development. A small, weighted-base cup helps reduce spills when your baby sets it down.
If an open cup feels too messy, a straw cup without a spill-proof valve is the next best choice. Straw cups allow more natural tongue movement than traditional sippy cups. Spill-proof valves, while convenient, encourage a sucking motion similar to a bottle and don’t help your baby learn the sipping skill they’ll need long-term.
Expect spills. You can help by lifting the cup to your baby’s lips yourself at first, offering just a small amount of water in the cup so a spill isn’t a big deal. Keep your baby seated and supervised during practice, and offer the same drink (water) each time so the routine becomes familiar. Most babies take a few days to a couple of weeks to get comfortable with a new cup.
What Not to Offer
Plain water is the only additional drink your baby needs at this age besides breast milk or formula. Juice, flavored water, and sugary drinks are not recommended for babies under 12 months. Very cold drinks can be startling and uncomfortable. And you should never dilute formula with extra water to stretch it further. Diluted formula delivers fewer calories, vitamins, and minerals per feeding, putting your baby at risk for poor weight gain and nutritional deficiencies.