A 10-month-old needs about 4 to 8 ounces of water per day, which works out to roughly half a cup to one cup. That’s less than most parents expect. At this age, breast milk or formula still supplies the majority of your baby’s fluids, so water is a small supplement rather than a primary drink.
Why the Amount Is So Small
Babies between 6 and 12 months get most of their hydration from breast milk or formula, both of which are predominantly water already. A 10-month-old drinking 24 to 32 ounces of milk per day is taking in plenty of fluid before water even enters the picture. The 4 to 8 ounces of plain water recommended on top of that is really just meant to help your baby get comfortable with drinking water and to wash down solid foods during meals.
As your baby eats more solids, those foods contribute water too. Fruits, vegetables, yogurt, and purees all contain significant moisture. So even if your baby only sips an ounce or two of water at mealtimes, they’re likely getting enough total fluid throughout the day.
When and How to Offer Water
The easiest approach is to offer a small amount of water with meals and snacks. Around 9 to 12 months, water during mealtimes helps babies learn to drink and can make swallowing thicker foods more comfortable. You don’t need to push it. Set the cup down, let your baby practice, and don’t worry if they only take a few sips.
For the cup itself, pediatric feeding specialists recommend two types: an open cup and a straw cup. Both build skills your baby will use for life. Open cups teach tilting and lip control, while straw cups develop suction with a sealed lip position. Traditional sippy cups and 360-degree cups are popular but encourage drinking patterns that babies outgrow quickly, making them less useful for long-term development. A small open cup with just an ounce of water at a time keeps spills manageable while your baby practices.
Too Much Water Is Risky
It might seem harmless to let your baby drink as much water as they want, but infants are genuinely vulnerable to water overload. Their kidneys are still maturing and can’t flush excess water as efficiently as an adult’s. When a baby takes in too much water relative to their body size, sodium levels in the blood drop rapidly, a condition called water intoxication.
Symptoms include unusual irritability or sleepiness, low body temperature, puffiness, and in serious cases, seizures. These problems can appear when total body water increases by as little as 7 to 8 percent, which doesn’t take much volume in a small infant. Sticking to the 4 to 8 ounce daily range and letting breast milk or formula remain the primary drink keeps your baby safely within normal limits.
One common scenario to watch for: diluting formula with extra water to stretch it. This reduces the nutrient concentration and increases the risk of water overload at the same time. Always mix formula according to the package directions.
Signs Your Baby Is Well Hydrated
Six to eight wet diapers a day is the normal range for a well-hydrated infant. If your baby consistently has fewer than three or four wet diapers in 24 hours, that suggests dehydration. Other signs to watch for include a dry mouth, fewer tears when crying, and unusual fussiness or lethargy. During hot weather, illness, or bouts of vomiting and diarrhea, your baby loses fluid faster than usual. In those situations, extra breast milk or formula feedings are typically more effective than plain water for replacing both fluids and electrolytes.
Tap Water, Fluoride, and Safety
Fluoridated tap water is safe for infants, according to the American Dental Association. If your baby drinks small amounts of water from the tap or you use tap water to prepare formula, the fluoride exposure at this age is not a concern for most families. In rare cases, babies who drink large volumes of powdered formula mixed with fluoridated water may develop mild fluorosis, which shows up later as faint white spots on the teeth. It’s cosmetic and doesn’t affect how the teeth work. If this worries you, using filtered or low-fluoride water for formula preparation is a reasonable option.
If your home has well water or older plumbing, having the water tested for lead and bacteria is worth the small cost. Boiling water kills pathogens but does not remove lead or other heavy metals.
What Changes After 12 Months
Water needs increase once your baby turns one. At that point, whole milk replaces formula or becomes the primary dairy source alongside continued breastfeeding, and water becomes a more regular part of daily intake. Most toddlers between 12 and 24 months need around 8 to 32 ounces of water per day depending on their size, activity level, and how much milk they drink. The jump from the 4 to 8 ounce range happens naturally as solids become the main source of nutrition and milk feedings decrease. For now, at 10 months, keeping water small and supplemental is exactly the right approach.