At 8 months old, your baby can have 4 to 8 ounces of water per day, which works out to about half a cup to one cup. That’s the range recommended by both the CDC and the American Academy of Pediatrics for babies between 6 and 12 months. It’s a small amount on purpose, and understanding why helps you get the balance right.
Why the Limit Is So Low
Your baby’s primary nutrition and hydration still come from breast milk or formula at this age. Those liquids provide calories, fat, protein, and fluid all in one package. Water has zero calories, but it still fills up a small stomach. If your baby drinks too much water, they feel full and take in less milk, which means fewer of the nutrients they need to grow.
Think of water at 8 months as a complement to meals, not a replacement for milk feeds. A few sips with solid food is the sweet spot. You’re building a habit, not meeting a hydration quota.
What Water Intoxication Looks Like
Babies are more vulnerable to water intoxication than adults because their kidneys are still maturing. When an infant takes in too much water too quickly, sodium levels in the blood drop. This causes cells to swell, particularly in the brain. The CDC has documented cases where symptoms included unusual irritability or sleepiness, low body temperature, facial puffiness, and in severe cases, seizures. These symptoms follow a rapid drop in blood sodium caused by an acute overload of water that increases total body water by roughly 7% to 8% or more.
Staying within the 4 to 8 ounce daily range makes this outcome extremely unlikely. The risk comes from dramatically exceeding that amount, such as diluting formula with extra water or offering water as a primary drink throughout the day.
When and How to Offer Water
The easiest approach is to offer a small amount of water at mealtimes, alongside solid foods. A few sips with breakfast and a few sips with dinner is plenty. You don’t need to track ounces precisely. If your baby takes a sip or two and loses interest, that’s fine. If they drink a couple of ounces with a meal, that’s also fine.
What matters more than the cup is the type of cup. Pediatric feeding specialists recommend starting with an open cup, even at this age. It teaches your baby to close their lips around the rim, take a small sip, and swallow, skills that support both feeding development and speech. A straw cup is a great second option and also promotes healthy oral-motor patterns. Hard-spout sippy cups are the least ideal choice because they can interfere with proper tongue positioning that’s important for speech development. A 360-degree cup (the kind with a silicone membrane lid) works similarly to an open cup with less mess, though a standard open cup gives the best practice.
Expect spills. Pour just an ounce or so into the cup at a time so cleanup stays manageable.
Signs Your Baby Is Well Hydrated
You don’t need to worry about counting water ounces if your baby is getting enough breast milk or formula. The most reliable hydration check is diaper output. At this age, look for at least 4 to 5 thoroughly wet disposable diapers (or 5 to 6 cloth diapers) in a 24-hour period. The diapers should feel heavy and genuinely soaked, not just damp.
Other signs of good hydration include tears when crying, a moist mouth, and skin that springs back quickly when gently pinched. If you notice significantly fewer wet diapers, dark yellow urine, or a sunken soft spot on your baby’s head, those are signs to increase milk feeds and contact your pediatrician.
Tap Water, Filtered Water, and Fluoride
In most of the U.S., tap water is safe for an 8-month-old. Community water supplies are typically fluoridated at 0.7 milligrams per liter, a level that helps protect developing teeth. A 2024 review by the National Toxicology Program found that fluoride levels above 1.5 milligrams per liter (the World Health Organization’s upper safety limit) were associated with lower IQ scores in children. At the 0.7 mg/L level used in U.S. water systems, there wasn’t enough data to determine any negative effect.
If you’re on well water, it’s worth testing for fluoride levels and contaminants since wells aren’t regulated the same way municipal supplies are. Bottled water is generally unnecessary, but if you use it, check the label for fluoride content and avoid brands marketed as “purified” that may have had fluoride removed entirely, since your baby’s teeth benefit from some exposure.
What Not to Give at 8 Months
Water is the only additional drink your baby needs beyond breast milk or formula at this stage. Avoid juice, flavored water, sweetened drinks, and cow’s milk as a primary drink before 12 months. Juice offers sugar without the fiber found in whole fruit, and cow’s milk doesn’t have the right nutrient balance for babies under one year. Plain water in small amounts alongside milk feeds is all your baby needs until their first birthday, when whole milk and slightly more water enter the picture.