When can babies drink water? A hydration guide by age

In this article

1. The short answer, by age
2. Why babies under 6 months shouldn't drink water
3. Water intoxication: the risk parents rarely hear about
4. Around 6 months: introducing the first sips
5. How much water after 6 months
6. After the first birthday: water becomes a main drink
7. Hot weather, fever, and the "but it's so warm" question
8. Signs your baby is well hydrated — and when to call

It feels like the most natural instinct in the world: it's a warm morning, the baby seems thirsty, so you reach for a little water. But for the first half-year of life, plain water is one of the few everyday things a baby genuinely should not have — and giving too much can be dangerous, not just unnecessary. The good news is that the rules are simple once you know them, and they change in clear steps as your baby grows.

The short answer, by age

Hydration needs shift in three broad stages: the milk-only newborn months, the "small sips with solids" window from around six months, and the toddler stage where water becomes a normal everyday drink. Here is the at-a-glance version, drawn from American Academy of Pediatrics (AAP), CDC, and NHS infant-feeding guidance.

Age	Where hydration comes from	Plain water?	Rough water amount
0–6 months	Breast milk or formula only	No	None — milk covers all fluid needs
6–12 months	Breast milk/formula + solids	Small sips with meals	About 4–8 oz (0.5–1 cup) a day
12–24 months	Whole milk + water + food	Yes, freely	About 1–4 cups a day
2 years and up	Water as the default drink + milk	Yes	Roughly 1–5 cups, more when active or hot

Hydration benchmarks synthesized from AAP / HealthyChildren.org, CDC infant nutrition, and NHS baby-feeding guidance. Amounts are general ranges, not targets to hit precisely.

The single most important line in that table is the first one. Before six months, a healthy baby needs no water at all — and offering it can do real harm. Here is why.

Why babies under 6 months shouldn't drink water

Breast milk and formula are not just food; they are about 87 percent water. A baby who is feeding well is already fully hydrated, even in summer. The AAP and CDC are consistent on this: infants under six months should be given only breast milk or formula, with no additional plain water, unless a pediatrician advises otherwise for a specific medical reason.

There are two problems with adding water in these early months. The first is nutritional. A newborn's stomach is tiny, so a few ounces of water can blunt their appetite and displace the calories and nutrients they actually need from milk — which, over time, can affect weight gain. The second problem is more serious, and far less well known.

Water intoxication: the risk parents rarely hear about

A young baby's kidneys are still developing and cannot process large volumes of water the way an adult's can. When an infant takes in too much plain water, it can dilute the sodium in their blood — a condition called hyponatremia, sometimes described as water intoxication. In mild cases it can cause irritability, drowsiness, or a low body temperature; in severe cases it can lead to swelling in the brain and seizures.

This is why pediatric guidance is firm rather than cautious about water before six months. It is also why two practices deserve a specific warning: never dilute formula with extra water beyond the instructions on the tin, and don't offer bottles of water to "top up" a young baby in hot weather. Both can push water intake past what a small body can safely handle.

“For the first six months, the safest drink for your baby isn't water — it's more milk. Their bottle is already mostly water.”

Around 6 months: introducing the first sips

Things change when your baby starts solid foods, usually around six months. At this point small amounts of water alongside meals are not only safe but helpful — both for hydration as solids reduce the proportion of fluid from milk, and for learning the skill of drinking from a cup. Breast milk or formula still does the heavy lifting; water is a complement, not a replacement.

The how matters as much as the what. Pediatric and dental guidance favors offering water in an open cup or a free-flow (straw or spout) cup rather than a no-spill valved sippy cup, which encourages constant sipping and can affect tooth and speech development. Plain tap water (in areas where it's safe to drink) or boiled-and-cooled water is fine; there's no need for special baby water for healthy sipping.

How much water after 6 months

From six to twelve months, most guidance points to a small, steady amount: roughly four to eight ounces of water a day, offered in sips with meals rather than all at once. There's no need to push it. If your baby takes a few sips and turns away, that's normal — their milk feeds are still meeting most of their fluid needs.

A few practical notes for this window:

• Offer with meals. A cup of water beside solid food helps with swallowing and builds the habit naturally.
• Don't replace milk feeds. Water should sit alongside breast milk or formula, not in place of them, until after the first birthday.
• Skip juice and sweetened drinks. The AAP recommends no fruit juice at all under 12 months; water and milk are all a baby needs.
• Let appetite lead. Some babies drink more, some less — wet diapers and pale urine tell you more than the ounces in the cup.

After the first birthday: water becomes a main drink

At twelve months the picture opens up. Water and whole cow's milk become the two main drinks, and water can now be offered freely throughout the day. Toddlers roughly need on the order of one to four cups of water daily on top of their milk, with the exact amount varying by size, activity, weather, and how much fluid they're getting from food.

This is also the stage to make water the easy default. Keeping an open or straw cup of water within reach, offering it at meals and snacks, and steering away from juice and sweetened drinks all help set a hydration habit that lasts well beyond toddlerhood. If your toddler is busy and forgets to drink, gentle, regular offers work better than waiting for them to ask.

Hot weather, fever, and the "but it's so warm" question

The hot-weather question is the one that trips up the most parents, so it's worth being clear. For a baby under six months, the answer to a warm day is still not water — it's more frequent breast or formula feeds. Breastfed babies will often feed more briefly and more often to quench thirst, and that's exactly how it should work. Formula-fed babies can be offered their usual feeds more often.

Fever, vomiting, or diarrhea in a young baby is a different situation and not a do-it-yourself one. Extra fluids in those cases — including whether and how to use an oral rehydration solution — should be guided by your pediatrician, because a sick infant can become dehydrated quickly and plain water is not the right fix. The rule of thumb: when your baby is unwell, the question isn't "how much water," it's "time to call."

Signs your baby is well hydrated — and when to call

You don't need to measure milliliters to know your baby is getting enough fluid. The body gives clear signals. Reassuring signs of good hydration at any age include:

• Regular wet diapers — broadly around six or more a day once feeding is established
• Pale, mild-smelling urine rather than dark and strong
• A baby who is alert, feeding well, and content

On the other side, certain signs of possible dehydration warrant a prompt call to your pediatrician — same day, or urgent care if your clinic is closed. The AAP, NHS, and CDC consistently flag: noticeably fewer wet diapers or a dry stretch of six hours or more, dark urine, a sunken soft spot (fontanelle), dry lips or mouth, crying with few or no tears, and unusual sleepiness or trouble feeding. Dehydration moves fast in babies, so when in doubt, call — with your recent feeds and diaper counts in hand.

This article is for general information and isn't a substitute for medical advice. Evidence summarized from AAP / HealthyChildren.org, CDC, and NHS guidance. Before giving water to a baby under 6 months, or if you're worried about hydration in a sick or very young baby, talk to your pediatrician.