An 8-month-old needs only 4 to 8 ounces of water per day, which is about half a cup to one cup. That small amount surprises many parents, but at this age, breast milk or formula still provides the vast majority of your baby’s hydration and nutrition. Water is a supplement to meals, not a primary drink.
Why the Amount Is So Small
Breast milk and formula are roughly 80 to 90 percent water. Every feeding your baby takes is already a hydration session. At 8 months, your baby is likely drinking 24 to 32 ounces of breast milk or formula daily, which covers their fluid needs almost entirely. The 4 to 8 ounces of water recommended by the American Academy of Pediatrics is really just meant to help your baby get comfortable with drinking water, practice using a cup, and wash down solid foods.
Offering too much water can actually backfire. Water has no calories or nutrients, so if your baby fills up on it, they may drink less breast milk or formula. That means fewer of the calories, fat, and nutrients they need for rapid brain and body growth during this stage.
When and How to Offer Water
The simplest approach is to offer a few sips of water with meals. Once your baby is eating solid foods, a small amount of water at mealtimes helps with swallowing and digestion. You don’t need to track ounces precisely. Just put a small amount in a cup and let your baby practice drinking from it during meals. Some babies will take a few sips, others will barely touch it. Both are fine.
Between meals, breast milk or formula should remain the go-to drink. Water shouldn’t replace any feedings, and there’s no need to offer it when your baby is thirsty outside of mealtimes. Breast milk or formula handles that job until at least 12 months.
Choosing the Right Cup
An open cup or a straw cup are both good options at 8 months. Open cups help develop the oral motor skills your baby will use for years. Straw cups build similar skills and tend to be less messy. Traditional sippy cups with a spout work in a pinch, but they use the same sucking motion as a bottle, so they don’t encourage as much developmental progress. If your baby is just starting out, expect spills. That’s part of the learning process, and it’s another reason to keep the volume small.
The Risk of Too Much Water
Babies under 12 months are vulnerable to a condition called water intoxication. Their kidneys are still immature, and too much water dilutes the sodium in their blood. This can cause seizures, brain swelling, and in rare cases, serious harm. The risk is highest in babies under 9 months.
There’s no precise “danger threshold” published in ounces, but the general guidance is clear: stick to the 4 to 8 ounce daily range, offer water only after your baby has satisfied their hunger with breast milk or formula, and never give large volumes at once. If you feel your baby needs extra water (during hot weather, for example), limit it to 2 to 3 ounces at a time.
What About Other Drinks?
Breast milk or formula and small amounts of water are the only drinks your 8-month-old needs. Cow’s milk can be used in cooking or mixed into foods at this age, but it shouldn’t be offered as a drink until 12 months because it doesn’t have the right balance of nutrients for an infant. Juice, flavored water, and plant-based milks are also off the table for now.
Signs Your Baby Is Well Hydrated
The easiest way to check hydration is wet diapers. A well-hydrated 8-month-old typically produces 6 or more wet diapers per day. The urine should be pale yellow or nearly clear. If you’re seeing that consistently, your baby is getting enough fluid from breast milk, formula, and their small amount of water combined.
Signs of dehydration to watch for include:
- Fewer wet diapers than usual or dark yellow urine
- A sunken soft spot (fontanelle) on top of the head
- Sunken eyes
- Few or no tears when crying
- Unusual drowsiness or irritability
Dehydration in infants most commonly happens during illness, particularly with vomiting or diarrhea. If your baby is sick and showing any of these signs, that warrants prompt medical attention. During normal healthy days, as long as breast milk or formula intake is on track, dehydration is uncommon.
A Typical Day at 8 Months
To put this all together practically: your baby’s day still revolves around breast milk or formula as the main source of nutrition and hydration. Solid foods are growing in importance but haven’t taken over yet. At each meal of solids (most 8-month-olds eat two to three times a day), you can offer a small open cup or straw cup with an ounce or two of water. Your baby may drink it, play with it, or ignore it entirely. All of that is normal. The total water from the cup across the whole day should land somewhere around 4 to 8 ounces, and there’s no need to push it beyond that.