An 8-month-old needs only 4 to 8 ounces of water per day. That’s roughly half a cup to one cup, offered in small sips throughout the day alongside breast milk or formula, which remain the primary sources of hydration until age one.
Why the Amount Is So Small
Breast milk is about 87 to 88 percent water, and prepared formula has a similar composition. Every time your baby nurses or takes a bottle, they’re getting most of the fluid they need. The 4 to 8 ounces of plain water recommended by the CDC is meant to complement those feedings, not replace them. Think of it as practice with a new drink rather than a hydration strategy.
At 8 months, your baby’s kidneys are still maturing. They can’t process large volumes of plain water the way an older child’s kidneys can. Too much water dilutes the sodium in the blood, a condition called water intoxication. Symptoms include unusual irritability or sleepiness, low body temperature, swelling, and in severe cases, seizures. This risk is highest in very young infants under 6 months, but it still applies at 8 months if water intake is excessive. Sticking to the 4 to 8 ounce range keeps things safe.
When and How to Offer Water
The easiest approach is to offer a few sips of water at mealtimes, when your baby is already sitting down with solid foods. If your baby eats three small meals a day, a couple of ounces at each meal gets you into the recommended range without overthinking it. You don’t need to track every sip precisely.
This is also a good time to introduce a cup. Open cups with two handles are easier for small hands to grip. You can also try straw cups or sippy cups to see what your baby prefers. Start with just a small splash of water in the cup and let your baby explore it. Expect spills. Tip the cup gently to help them feel the water on their lips. Drinking from a cup at the table while your baby watches is one of the best ways to teach by example, since babies at this age love to imitate.
Increase the amount of liquid in the cup gradually as your baby gets more coordinated. There’s no rush. The goal right now is familiarity with the cup and the taste of water, not hitting a hydration quota.
What Type of Water to Use
Plain tap water is fine for most 8-month-olds, and municipal tap water has the advantage of containing fluoride, which supports developing teeth. Some guidelines recommend boiling and cooling tap water for babies under 12 months, particularly if you’re on well water or tank water rather than a treated municipal supply. If your home uses a filtration system, boiling before serving is a good precaution since filters can harbor bacteria over time.
Bottled water isn’t necessary unless your tap water is under a safety advisory. If you do use bottled water, avoid mineral water. It contains higher levels of salt and minerals that an infant’s kidneys aren’t equipped to handle well.
Signs Your Baby Is Getting Enough Fluid
You don’t need to worry much about dehydration in an 8-month-old who is nursing or taking formula regularly and eating some solid foods. The clearest indicators that hydration is on track are wet diapers (at least four to six per day), tears when crying, and a moist mouth. If your baby seems content after feedings and is producing plenty of wet diapers, their total fluid intake from milk and those few ounces of water is doing the job.
During hot weather or if your baby has a fever or diarrhea, you may notice them wanting to nurse or take a bottle more frequently. Extra breast milk or formula is the best way to make up for fluid losses at this age, rather than significantly increasing plain water. A few additional sips of water are fine, but the bulk of rehydration should come from milk feeds.
Drinks to Avoid at 8 Months
- Juice: Even 100 percent fruit juice adds sugar without the fiber of whole fruit. It can also displace breast milk or formula in your baby’s diet.
- Cow’s milk as a drink: Cow’s milk isn’t recommended as a primary beverage until 12 months. It’s difficult for younger babies to digest properly and doesn’t have the right balance of nutrients.
- Flavored water or electrolyte drinks: These contain added sugars or artificial sweeteners that your baby doesn’t need.
- Herbal teas: Some herbal ingredients can be harmful to infants, and the water volume from tea could push total intake too high.
At 8 months, the drink menu is simple: breast milk or formula as the main event, and a few ounces of plain water on the side for practice.