A 10-month-old needs about 4 to 8 ounces of water per day, which is roughly half a cup to one cup. That’s the recommendation from the American Academy of Pediatrics for all babies between 6 and 12 months. It’s a small amount because breast milk or formula is still doing the heavy lifting for hydration and nutrition at this age.
Why the Amount Is So Small
At 10 months, your baby is eating more solid foods than they were a few months ago, but breast milk or formula remains the primary source of both calories and fluids. Most babies this age eat or drink about 5 to 6 times in a 24-hour period, and as they gradually take in more solids, they naturally need a little less formula or breast milk. Water fills in the gaps, especially during meals, but it’s not meant to replace milk feeds.
The 4 to 8 ounce range is a guideline, not a strict target. Some days your baby might drink closer to 4 ounces, other days closer to 8. That’s normal. The goal is to offer water in small amounts throughout the day rather than giving a large volume at once.
When and How to Offer Water
The easiest approach is to offer a few sips of water with meals and snacks. You don’t need to track every ounce precisely. Just keep a cup accessible when your baby is eating solids, and let them drink as much or as little as they want within that 4 to 8 ounce daily range.
For the cup itself, speech and feeding specialists generally recommend skipping traditional sippy cups. A straw cup is a better choice because it encourages a more mature swallowing pattern where the tongue rises naturally. An open cup (with your help) is also excellent practice, and most experts suggest introducing one before your baby’s first birthday. The ideal progression is breast or bottle, then straw cup, then open cup.
Risks of Too Much Water
Giving a baby too much water can cause a condition called water intoxication, where sodium levels in the blood drop dangerously low. This happens because an infant’s kidneys are still developing and can’t flush large volumes of water the way an adult’s can. At 10 months the risk is lower than it is for younger babies, but it’s still real if water significantly displaces milk feeds or if a baby is given large amounts at once.
The most common ways this happens are diluting formula with extra water to stretch supplies, or offering water as a substitute for breast milk or formula. Always mix formula according to the manufacturer’s instructions, and treat water as a complement to milk feeds, not a replacement.
Tap Water, Well Water, and Fluoride
Municipal tap water is generally safe for a 10-month-old. If your home uses a private well, the EPA recommends testing the water and avoiding it for mixing with formula or food if nitrate levels exceed 10 milligrams per liter. When you’re unsure about well water quality, bottled water or water from a tested public supply is a safer choice.
Fluoridated tap water is considered safe and effective for preventing tooth decay, according to the AAP, ADA, and CDC. If your water supply doesn’t contain fluoride, or you use well water without it, ask your pediatrician whether your baby might benefit from fluoride drops or tablets. This is especially relevant if your child is at higher risk for cavities.
Signs Your Baby Needs More Fluids
Even with the right amount of water and regular milk feeds, babies can sometimes become dehydrated, especially during illness, hot weather, or bouts of vomiting or diarrhea. Watch for these signs:
- Fewer wet diapers than usual or noticeably darker urine
- A sunken soft spot on the top of the head
- Sunken eyes or few to no tears when crying
- Unusual drowsiness or irritability
If you notice any of these, increasing breast milk or formula is the first step, since those provide electrolytes and calories along with fluid. A few extra sips of water can help too, but milk remains the better rehydration tool at this age. Persistent signs of dehydration warrant a call to your pediatrician.