When can babies drink water? Not before 6 months, then sips

In short

Under 6 months: no water, tea or juice. Breast milk or formula covers thirst (AAP, WHO).
Hot weather: offer more milk feeds. The NHS adds that a formula-fed baby under 6 months may be given small sips of cooled boiled water in hot weather; fully breastfed babies need none.
From about 6 months: a little water from an open or free-flow cup with meals, 4–8 oz (120–240 ml) a day at most (AAP, NHS).
No juice before 12 months, and no tea, sweetened drinks or honey (AAP, NHS).
From 12 months: water and whole milk are the drinks, about 16 oz (2 cups) of milk a day (AAP).

Water by age

Age	Water	Why
0–6 months	none	Milk is all they need; water fills a tiny tummy without calories or nutrients.
6 months	a few sips with meals	Practice with a cup as solids start (NHS, AAP).
7–12 months	up to 4–8 oz (120–240 ml) a day	The AAP's upper limit while milk is still the main drink.
12 months +	water with meals and between	Water and milk are the recommended drinks (AAP).

Why no water before 6 months

Milk is mostly water already. The AAP recommends breast milk as a baby's only food for about the first 6 months, and the WHO recommends exclusive breastfeeding for 6 months; neither adds water. In maternity care, the WHO's standards say to avoid giving babies any other food or drink, "even water", unless medically necessary.

Water takes the place of milk. A young baby's stomach is small. Water fills it without the calories and nutrients they need.

Too much water can be dangerous. Infants given large amounts of water can develop water intoxication, a dangerous drop in blood sodium. In one US hospital's series, most cases were babies given water because the family had run out of formula (Keating 1991). Never water down formula to stretch it; if you're struggling to buy formula, tell your pediatrician or WIC office.

Hot weather. A breastfed baby needs more feeds, not water. For formula-fed babies under 6 months, the NHS says small sips of cooled boiled water may be needed in hot weather, on top of their usual milk; US guidance doesn't add water. Ask your pediatrician if you're unsure.

From 6 months: how much water

Around 6 months you can start offering a little water, 4–8 ounces (½–1 cup) a day (AAP), in sips with meals from an open cup or a free-flow cup without a valve, which helps your baby learn to sip (NHS). Healthy babies don't need extra water beyond that; the AAP says to keep it to no more than about 1 cup (8 ounces) a day while milk is the main drink. From 6 months, tap water doesn't need to be boiled first (NHS).

What not to give

Juice: not before 12 months (AAP, Heyman 2017). The NHS says babies under 12 months don't need juice or smoothies.
Tea and coffee: not suitable for babies or young children (NHS). Herbal "colic" remedies have no evidence that they help (NHS).
Sweetened drinks: sodas, sports drinks, fruit drinks, sweetened water and other drinks with added sugar are harmful to a child's health (AAP). Squash, flavored milk and fizzy drinks aren't suitable for young babies (NHS).
Honey (even a dab on a pacifier): not before 1 year, because it can cause infant botulism (NHS).
Cow's milk as a drink: not before 12 months (AAP, NHS); a little in cooking is fine from around 6 months (NHS).
Plant milks: other than soy, not recommended in place of dairy milk for young children (AAP); rice drinks not under 5 years (NHS).

When to call the doctor

Signs of dehydration in a baby: a sunken soft spot on the head, sunken eyes, few or no tears when crying, fewer wet diapers than usual, drowsiness or irritability (NHS). Call your pediatrician the same day. Call 911 if your baby is very hard to wake, breathing fast, or has pale, blotchy or bluish skin (the NHS's emergency signs). A fever of 100.4 °F (38 °C) or more under 3 months: call right away (AAP).

Questions

Can babies drink water at 4 months?

They don't need to: breast milk or formula covers thirst until about 6 months (AAP). In hot weather, give more milk feeds; the NHS says a formula-fed baby may have small sips of cooled boiled water on top.

Can babies drink water at 5 months?

Same as at 4 months: not needed yet. Water starts around 6 months, with solids (AAP, NHS).

How much water can a 6 month old have?

A few sips with meals, adding up to no more than 4–8 ounces (120–240 ml) a day (AAP).

Can I give my baby water for constipation or hiccups?

Under 6 months, ask your pediatrician first rather than giving water. Constipation in a baby under 8 weeks who hasn't pooped for 2–3 days is a reason to call (NHS).

Does a baby need water in hot weather?

A breastfed baby needs more feeds, not water. A formula-fed baby under 6 months may be offered small sips of cooled boiled water in hot weather (NHS). Watch for fewer wet diapers.

How much milk at each age: the baby feeding chart. Making bottles: how to prepare formula safely.

Sources

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