How Much Water Should a Baby Drink?

Under six months: none

Ireland's HSE is explicit. Breastfed babies get all the nourishment and hydration they need from your milk and do not need any other drinks. It states directly that breastfed babies do not need additional water, even in hot weather or when travelling to hotter countries. For formula-fed babies it says that first infant formula gives them the nourishment and hydration they need until age 1.

NHS guidance takes the same position, describing breast milk as the only food or drink babies need in the first six months of their life.

The reason this matters is not that water is dangerous in trivial quantities but that a young baby's stomach is small. Water displaces milk, and milk is where the calories and nutrients are. In hot weather the correct response is more frequent milk feeds, not water.

The exception

Cooled boiled water is sometimes advised for a young baby on medical advice, for example during illness or for constipation. That is a clinician's decision, not a routine measure, so follow the advice you are given rather than starting it yourself.

From six months: sips with meals

NHS guidance says to introduce your baby to drinking from a cup or beaker from around six months and offer sips of water with meals. It recommends using an open cup or a free-flow cup without a valve, because this helps your baby learn to sip and is better for their teeth, and notes it might be messy at first.

The HSE gives the same instruction, adding a practical point about preparation: offer your baby water in a cup at meals or snack times, and drinking water for babies over six months does not need to be boiled or sterilised first, though formula still needs to be prepared safely. It advises avoiding bottled water labelled as natural mineral water, because it can have higher levels of sodium and other minerals.

There is no target volume at this stage. Water is offered rather than measured, and milk is still the main drink. A baby who takes two sips and turns away has had enough.

From one year: the first actual figure

The HSE gives the only concrete number in this topic: most children aged 1 to 4 years need 6 to 8 glasses of fluid a day, and water is best. It adds that water, breast milk and milk are the best drinks to give children aged 1 to 4, and that there is no need to boil and cool water for children over age 1.

Fluid here includes milk, so a toddler having milk at breakfast and bedtime is already several glasses into the total. The figure is a guide rather than a quota to enforce, and needs rise in hot weather, during illness and with activity.

NHS guidance notes that cows' milk can be introduced as a main drink from 12 months, and that no special milks are needed once your baby is 12 months old, including first infant formula, follow-on formula, growing-up milks and toddler milks.

Drinks to avoid

The HSE says not to give a 0 to 12 month old baby fruit juice or squash, even diluted. NHS guidance makes the same point in the context of tooth decay, saying that avoiding sugary snacks and drinks, including fruit juice and other fruit drinks, helps prevent tooth decay.

NHS guidance on drinks and cups adds a specific warning about what goes in a bottle: do not put anything in a bottle or trainer cup other than breast milk, formula milk or water, and do not add anything else including sugar, cereals, baby rice or chocolate powder. It explains that comfort sucking from a bottle on sweetened drinks causes tooth decay in young children, because drinks flow very slowly through a teat, meaning the sugary substance is in contact with the teeth for longer.

The HSE warns against cows' milk as a main drink before age 1, noting that it can be difficult for babies to digest, can lead to health complications such as dehydration and iron deficiency, and does not have all the nutrients your child needs.

Signs of dehydration

NHS and HSE guidance both describe what to watch for in babies and children: fewer wet nappies than usual or dark, strong-smelling urine; a dry mouth and lips; no tears when crying; unusual drowsiness or irritability; sunken eyes; and in a young baby, a sunken soft spot on the top of the head. Cold or blotchy hands and feet, or fast breathing, indicate more severe dehydration.

Get urgent medical advice if your baby has fewer wet nappies, is unusually sleepy or floppy, is refusing feeds, is vomiting repeatedly and cannot keep fluids down, or has any of the more severe signs above. HSE guidance on dehydration in babies and children stresses that babies become dehydrated much more quickly than adults, which is why the threshold for seeking help is deliberately low.

Illness and hot weather

During diarrhoea and vomiting the priority is fluid, and for a young baby that means continuing milk feeds, more often and in smaller amounts, rather than switching to water. Oral rehydration solutions are sometimes recommended and should be used on the advice of a pharmacist, GP or health visitor rather than started independently for a baby.

In hot weather, offer breastfeeds or formula more frequently for under-sixes, and offer water more often alongside meals and snacks for older babies and toddlers. Keeping a baby out of direct sun and in cooler rooms does more than any drink to prevent overheating.