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 across the day. This small amount is enough to help your baby get used to water without interfering with the breast milk or formula that still provides nearly all of their nutrition and hydration.
Why Water Starts at 6 Months
Before 6 months, babies get all the hydration they need from breast milk or formula. Introducing water earlier can actually cause problems by replacing nutrient-rich milk in their tiny stomachs. Breast milk is about 87% water on its own, so even in hot weather, a younger infant who is feeding well doesn’t need supplemental water.
The 6-month mark lines up with the introduction of solid foods. As your baby starts eating purees or soft foods, small sips of water help wash things down and get them comfortable with drinking something other than milk. The water isn’t replacing a feeding. It’s a companion to meals.
Why the Limit Matters
A baby’s kidneys are still immature and can’t process large volumes of water the way an adult’s can. Too much water dilutes the sodium in their blood, a condition called hyponatremia. In infants, this can escalate quickly. Symptoms include vomiting, facial puffiness, unusual sleepiness or irritability, and in serious cases, seizures.
In one published case, a 5-month-old who was given about 3.4 ounces of water every three hours between formula feedings developed dangerously low sodium levels and had seizures. That may not sound like a huge volume, but for a small baby receiving it repeatedly throughout the day on top of formula, it was far too much. Sticking to the 4 to 8 ounce daily range and offering water only at mealtimes keeps you well within safe territory.
There’s also a nutritional concern. Every ounce of water that fills your baby’s stomach is an ounce of breast milk or formula they won’t drink. At 6 months, milk is still the primary source of calories, fat, protein, and vitamins. Too much water can quietly lead to a calorie deficit over time, slowing weight gain without any obvious red flags.
How to Offer Water
The best approach is to offer a few sips of water during meals, not between feedings. A small open cup, a sippy cup, or a straw cup all work. Open cups (including small training cups with two handles) are worth trying early because they help your baby develop drinking skills they’ll need later. Put only a small amount of water in the cup at first, maybe an ounce or two, and tip it gently so your baby can feel the liquid on their lips.
Don’t worry if your baby barely drinks any. At this age, it’s more about practice than hydration. Some babies will take a few sips and push the cup away. Others will be fascinated. Either response is normal. You can model the behavior by drinking from your own cup at family meals.
Tap Water, Filtered, or Bottled
Plain water is all your baby needs. There’s no reason to add juice, sugar, or flavoring. If your tap water is fluoridated, it actually provides a small benefit for developing teeth. If you’re on well water or unsure about your local supply, filtered or bottled water is a reasonable choice. Avoid mineral water or sparkling water, which can contain sodium or carbonation that isn’t appropriate for infants.
Signs Your Baby Needs More Fluids
The answer to low hydration in a 6-month-old is almost always more breast milk or formula, not more water. That said, it helps to know what dehydration looks like. Mild dehydration usually shows up as fewer wet diapers than usual (fewer than six in 24 hours is a common benchmark). Your baby may seem a bit fussier than normal.
Moderate dehydration brings more noticeable signs: a dry mouth, skin that doesn’t bounce back quickly when gently pinched, faster heart rate, and increased irritability. In severe cases, babies become lethargic, their skin may look mottled, and the soft spot on the top of their head (the fontanelle) can appear sunken. If you notice any of these signs beyond mildly reduced wet diapers, increasing milk feeds is the first step, and persistent symptoms need medical attention.
Quick Reference by Age
- 0 to 6 months: No water needed. Breast milk or formula provides full hydration.
- 6 to 12 months: 4 to 8 ounces of water per day, offered in small amounts at mealtimes alongside continued breast milk or formula.
- 12 months and older: Water intake can gradually increase as your toddler transitions to more solid foods and whole milk.
The 4 to 8 ounce range gives you flexibility. On a hot day or when your baby is eating more solids, lean toward the higher end. On a day when they’re nursing or bottle-feeding frequently and only nibbling at food, a few sips is plenty.