A 6-month-old can have 4 to 8 ounces of water per day, according to the CDC. That’s roughly half a cup to one cup total, spread throughout the day. Before 6 months, babies don’t need any water at all because breast milk or formula provides all the hydration they require.
Why Water Starts at 6 Months
The timing isn’t a coincidence. Six months is when most babies begin eating solid foods, and small sips of water help wash down purees and soft foods. Before this point, breast milk and formula are about 80 to 90 percent water, so there’s no gap to fill.
Even after 6 months, water is a supplement, not a replacement. Breast milk or formula remains the primary source of both nutrition and hydration through the first year. The 4 to 8 ounces of water is meant to complement milk feedings, not compete with them. If a baby fills up on water, they may drink less milk and miss out on the calories, fat, and nutrients they need to grow.
Risks of Giving Too Much Water
Babies are small, and their kidneys are still maturing. Drinking too much water dilutes the sodium and other electrolytes in their blood, a condition called water intoxication. When sodium levels drop too low, water moves into cells and causes them to swell. In the brain, that swelling increases pressure and can lead to drowsiness, irritability, and in severe cases, seizures.
Early signs of water intoxication include nausea, bloating, and unusual fussiness. Muscle weakness, confusion, and swelling in the hands or feet can follow. These symptoms are rare when you’re sticking to the 4 to 8 ounce guideline, but they’re the reason that guideline exists. More water is not better for a baby this age.
Hot Weather and Illness
Parents often wonder if babies need extra water on hot days. Research published in Frontiers in Pediatrics reviewed studies of infant hydration in warm climates and found that exclusively breastfed infants maintained normal hydration levels even in hot conditions, without needing supplemental water. Breast milk naturally adjusts its water content during feeds.
For babies 6 months and older who are eating solids, offering water on the higher end of the range (closer to 8 ounces) on warm days is reasonable. But the answer isn’t to push past the recommended amount. Instead, continue offering breast milk or formula frequently. If your baby is sick with vomiting or diarrhea, the priority is maintaining milk feedings rather than adding extra water, since milk provides both fluids and electrolytes.
Signs of Dehydration to Watch For
Knowing the signs of dehydration matters more than hitting an exact water target. In mild to moderate dehydration, you’ll notice fewer than six wet diapers per day, a dry mouth, fewer tears when crying, and less interest in playing. The soft spot on top of your baby’s head may look slightly sunken.
Severe dehydration looks more alarming: extreme fussiness or excessive sleepiness, sunken eyes, cool or discolored hands and feet, wrinkled skin, and only one or two wet diapers in a full day. These signs call for immediate medical attention.
How to Offer Water
Six months is a good time to introduce a cup rather than putting water in a bottle. An open cup is the best choice for development. It teaches babies to form their lips around the rim and sip, which supports healthy oral and speech development in ways that sucking from a bottle or sippy cup does not.
If an open cup feels too messy (and it will be messy), a straw cup without a spill-proof valve is the next best option. Straw cups allow more natural tongue movement than traditional sippy cups. The American Dental Association recommends avoiding spill-proof cups and 360-degree cups because they encourage sucking rather than sipping and don’t teach babies how to regulate their own intake. If you use a lidded cup, choose one with a snap-on or screw-on lid and no valve.
Keep the portions tiny. You’re not trying to get your baby to finish a certain amount. Offer a few sips with meals, and let your baby decide when they’ve had enough. At this age, learning to drink from a cup is just as important as the water itself.
What Counts as “Water”
Plain water is the only thing that should go in your baby’s cup at this age. Juice, flavored water, and sweetened drinks are not recommended for babies under 12 months. Breast milk and formula still make up the vast majority of your baby’s daily fluid intake, typically 24 to 32 ounces per day, and those feedings should stay on their usual schedule.
A practical way to think about it: water is a side item at mealtimes, not a main course. A few ounces with breakfast, a few with dinner, offered in a small cup your baby can practice holding. The goal is gentle exposure, not a hydration quota.