A 10-month-old can have 4 to 8 ounces of water per day, spread across meals and snacks. That’s roughly half a cup to one cup total for the entire day. At this age, breast milk or formula is still your baby’s primary source of both nutrition and hydration, so water plays a supporting role rather than a starring one.
Why the Range Is 4 to 8 Ounces
The CDC recommends 4 to 8 ounces of water daily for babies between 6 and 12 months old. That range accounts for differences in body size, how much solid food your baby eats, and how much breast milk or formula they’re still taking in. A 10-month-old who nurses frequently and eats watery foods like fruits and purées may only need a few sips at mealtimes. One who eats more dry solids, like crackers or cereal puffs, may benefit from the higher end of that range.
The key principle: water supplements your baby’s diet. It doesn’t replace any breast milk or formula feedings. If your baby starts filling up on water, they may drink less milk, which means fewer calories, less fat, and less protein during a period of rapid brain and body growth.
What Happens if a Baby Gets Too Much Water
Babies under one year are vulnerable to a condition called water intoxication. Their kidneys are small and still maturing, so they can’t flush out large volumes of water the way an adult’s kidneys can. When a baby takes in more water than their body can process, sodium levels in the blood drop. That sodium dilution disrupts how cells function, particularly in the brain.
Early signs include unusual irritability or sleepiness, low body temperature, and puffiness or swelling. In severe cases, a rapid drop in sodium can cause seizures. This doesn’t happen from a few extra sips at dinner. It typically results from consistently replacing milk feedings with water, diluting formula with extra water, or giving large bottles of water between feedings. Cleveland Clinic notes that babies under one year shouldn’t have more than about 3 ounces of water at any single sitting, reinforcing the idea that small amounts spread throughout the day are safer than one large serving.
How to Offer Water at This Age
The simplest approach is to offer a small amount of water with meals and snacks, not between feedings. Put an ounce or two in a cup at mealtime and let your baby sip as they eat. This helps wash down solid foods and gets them used to drinking water as part of a routine.
At 10 months, your baby is at a great age to start practicing with an open cup. Small, two-handled training cups work well because they’re easy to grip. Let your baby explore the cup before filling it. The first several attempts will mostly end up on their bib, and that’s fine. Tipping the cup gently so they feel the water touch their lips helps them learn the motion. Drinking from your own cup at the table gives them a model to imitate.
Sippy cups and straw cups are also fine, especially when spills are a concern. But practicing with an open cup early builds coordination and oral motor skills that matter for feeding development down the road.
Hot Weather and Illness
On very hot days, your baby loses more fluid through sweat, so extra hydration helps. The best first step is offering more frequent breast milk or formula feedings, since those provide both fluid and electrolytes. You can also offer small additional sips of water between feedings. The same applies during illness, especially if your baby has a fever or diarrhea. More frequent milk feedings should come first, with a little extra water as a supplement.
If your baby seems unusually fussy, isn’t producing tears when crying, or is having noticeably fewer wet diapers, those are signs of dehydration. A well-hydrated baby typically has six to eight wet diapers a day. Fewer than three or four is a signal to take seriously. In babies whose fontanelle (the soft spot on top of the head) is still open, a sunken or noticeably depressed soft spot can indicate more significant dehydration.
Signs Your Baby Is Getting Enough Fluid
You don’t need to measure every ounce precisely. The best indicators are practical ones: consistent wet diapers throughout the day, normal energy levels, and steady weight gain at checkups. A 10-month-old getting regular breast milk or formula feedings plus a few ounces of water with solids is almost certainly well hydrated.
If your baby refuses water from a cup, don’t force it. They’re likely getting plenty of fluid from milk and from water-rich foods like melon, peaches, yogurt, and cooked vegetables. The 4 to 8 ounce guideline includes all water, not just what comes from a cup.