A 10-month-old can safely drink 4 to 8 ounces of water per day, which is about half a cup to one cup. This recommendation from the American Academy of Pediatrics applies to all babies between 6 and 12 months old. It may sound like a small amount, but at this age, breast milk or formula is still your baby’s primary source of hydration and nutrition. Water is a supplement, not a replacement.
Why the Limit Is So Low
Your baby’s kidneys are still maturing and can’t process large volumes of water the way an adult’s can. When an infant takes in too much water, it dilutes the sodium in their blood, a condition called water intoxication. This causes cells in the brain to swell, which can lead to seizures. Symptoms are triggered when excess water increases total body water by roughly 7% to 8% or more. While this risk is highest in babies under 6 months, it still applies to older infants whose kidneys haven’t fully developed.
There’s also a practical concern: water fills your baby’s stomach without providing calories or nutrients. Too much water can reduce appetite for breast milk, formula, and solid foods, all of which deliver the fat, protein, and vitamins a 10-month-old needs for growth.
Your Baby Already Gets Water From Food
At 10 months, your baby is likely eating a variety of solid foods, many of which contain significant water. Fruits like watermelon, strawberries, and peaches are mostly water. Yogurt, cooked vegetables, and purees all contribute to hydration. So the 4 to 8 ounces of plain water your baby drinks is on top of the fluid they’re already getting from meals and milk. Most 10-month-olds are well hydrated without needing to push extra water.
When and How to Offer Water
The best time to offer water is during meals and snacks. A few sips with solid food helps your baby practice drinking and can aid with swallowing thicker textures. You don’t need to track every ounce precisely. Just offer small amounts and let your baby decide how much to take.
At 10 months, most babies can drink from a straw cup, and many are becoming proficient with one. If you’re teaching straw drinking, start by holding a straw in water, covering the top with your finger to trap a small column of water, and releasing it into your baby’s mouth once they seal their lips around it. The straw should only go about a quarter inch into their mouth, resting at the tip of the tongue rather than pushing it down.
An open cup is another great option. Fill it nearly to the rim (about one inch below) so your baby doesn’t have to tip it far back, which keeps their mouth and the cup in better alignment. Have them seated in a highchair with the tray below their elbows and their feet supported. Expect spills. This is a motor skill they’re actively building.
Tap Water, Fluoride, and Safety
Plain tap water is fine for a 10-month-old in most areas. Fluoridated water at standard community levels (around 1 milligram per liter) poses no known health risks, and the chance of dental fluorosis from drinking water at this age is low. The critical window for fluorosis risk in permanent teeth comes later, when children are older. If you’re still concerned, water labeled as purified, distilled, or reverse osmosis filtered contains little to no fluoride.
Avoid flavored water, juice, and sweetened drinks. Stick to plain water only.
Hot Weather and Illness
You might wonder whether to give extra water on hot days or when your baby has a fever. For babies under 12 months, the primary strategy for staying hydrated is offering more breast milk or formula rather than loading up on water. These provide both fluids and electrolytes, which plain water does not. You can continue offering the usual 4 to 8 ounces of water, but increasing milk or formula feeds is more effective for preventing dehydration.
Signs Your Baby Is Well Hydrated
The simplest check is diaper output. A baby 4 months or older who has fewer than 3 wet diapers in a day may be dehydrated. Most well-hydrated 10-month-olds produce significantly more than that. Other signs of good hydration include moist lips, tears when crying, and normal energy levels. If your baby’s urine looks dark yellow, their mouth seems dry, or they become unusually sleepy or fussy, those are signals to increase fluid intake through breast milk or formula first, with water as a small addition.