Water in Infancy: Guidance by Age

Should babies drink water? The answer depends on their age and how they are fed. During hot weather, families may wonder whether their baby needs extra water to prevent dehydration. It is a reasonable concern, but for babies under six months, breast milk or correctly prepared infant formula usually provides all the fluid they need. There is a specific exception for formula-fed babies in particularly hot weather, when a few small sips of cooled, boiled water may be offered alongside their usual milk feeds.

Once complementary foods are introduced, from around six months, small sips of water can be offered with meals. Milk remains an important source of fluid and nutrition throughout the first year (NHS, 2021; First Steps Nutrition Trust, 2024, 2026).

Milk provides both fluid and nutrition

Breast milk contains more than 80% water and provides the fluid a young baby needs, alongside energy and nutrients. Its composition changes during a feed and in response to the baby's needs. Exclusively breastfed babies under six months do not need additional water, even in hot weather. They may want to breastfeed more frequently, often taking shorter feeds to satisfy their thirst. Offering the breast more often provides additional fluid without replacing the nutrition in breast milk (WHO, 2024).

Correctly prepared infant formula also provides the fluid and nutrition a baby needs. Formula must always be made using the correct amount of water and powder, following the manufacturer's instructions. Adding extra water to a feed changes its nutritional composition and can be dangerous (NHS, 2023).

Water before six months

For babies under six months, the usual recommendation is to meet fluid needs through breast milk or correctly prepared infant formula. Giving additional water can fill a baby's small stomach without providing energy or nutrients. If water replaces some of a milk feed, the baby may take in less of the nutrition needed for growth.

Giving too much water can also disturb the balance of sodium and other electrolytes in a young baby's body. This can cause water intoxication, also known as hyponatraemia, which can be serious. Young babies are particularly vulnerable because their kidneys are still developing and have a limited ability to regulate excess water (First Steps Nutrition Trust, 2024).

Breastfed babies

Exclusively breastfed babies under six months do not need additional water, including during hot weather. Offer breastfeeds in response to the baby's cues; feeds may become shorter and more frequent when it is hot.

Combination-fed babies

For babies receiving both breast milk and formula, continue offering their usual milk feeds. If the baby is also breastfeeding, offering the breast more frequently can provide additional fluid. Additional water is not routinely needed before six months and should not replace either breast milk or formula.

Exclusively expressed breast milk

Babies receiving expressed breast milk still receive the fluid they need from their milk. If a baby appears thirstier in hot weather, offer additional expressed breast milk. The person expressing may need to express more frequently to provide the additional milk required. Milk production is regulated by milk removal, so reducing expression can affect the amount of milk produced (Kent, Prime and Garbin, 2012).

For practical guidance, see How to Express Breastmilk and Antenatal Hand Expression.

Formula-fed babies

According to the NHS (2021), formula-fed babies under six months may need a few small sips of cooled, boiled water during particularly hot weather, in addition to their usual formula feeds. The guidance does not specify an exact volume. Water should be offered between milk feeds and should not be given in quantities that replace a feed.

Tap water must be boiled and allowed to cool before being offered to a baby under six months. Bottled water is not routinely recommended because it can contain higher levels of sodium or sulphate. Formula must always be prepared using the correct amount of water and powder. Never add extra water to a prepared feed or reduce the amount of powder (NHS, 2021, 2023; First Steps Nutrition Trust, 2024, 2026).

Introducing water alongside complementary foods

Once a baby is around six months and has started eating solid foods, small sips of water can be offered with meals. Water can be given in an open cup or a free-flow cup without a valve, allowing the baby to practise sipping.

There is no need to boil tap water for babies over six months. Breast milk or first infant formula should remain the main drink during the first year, continuing to provide important fluid and nutrition as solid food intake increases. There is no single prescribed volume of water that every baby aged six to twelve months needs. Offer small amounts with meals and allow the baby to decide whether they want to drink. Water should complement milk feeds and food, rather than displace them (NHS, 2021; SACN, 2018; First Steps Nutrition Trust, 2024).

Water and health concerns

Families sometimes consider offering water when a baby is constipated or unwell. The right approach depends on the baby's age, symptoms and level of hydration.

Constipation

Water is not a routine treatment for constipation in babies under six months. Changes in stool frequency can occur during infancy, particularly in breastfed babies, and infrequent stools do not necessarily mean a baby is constipated. Stool consistency and whether the baby is distressed or struggling to pass it are also relevant.

Once complementary foods have been introduced, small sips of water can be offered with meals. Persistent constipation, hard stools, blood in the stool or significant discomfort should be discussed with a healthcare professional rather than managed by simply increasing water (NICE, 2017).

For more information, see Infant constipation and dyschezia.

Vomiting and diarrhoea

Tummy bugs can cause vomiting and diarrhoea, resulting in fluid loss. Babies, particularly those under six months, can become dehydrated more quickly than older children.

Continue offering usual milk feeds. Breastfeeding can continue as often as the baby wants. If a baby is struggling to manage their usual bottle feeds, offer smaller, more frequent feeds to allow fluid to be absorbed more gradually and improve tolerance.

If vomiting or diarrhoea is frequent, the baby is unable to keep feeds down, has fewer wet nappies or appears unusually sleepy, seek medical advice promptly. Babies who are very young or seem seriously unwell need urgent assessment (NICE, 2009; NHS, 2024).

Fever and other illness

A baby with a fever may need more frequent milk feeds, particularly if they are feeding less than usual. For babies under six months, continue offering breast milk or correctly prepared formula rather than using plain water to replace milk feeds. For older babies, continue offering milk and their usual small sips of water alongside meals.

A baby who is feeding poorly, has fewer wet nappies or seems unusually sleepy may be becoming dehydrated. Seek medical advice if you are concerned, particularly if the baby is very young or has a persistent fever (NHS, 2024).

When to seek professional advice

Seek advice from a healthcare professional if a baby is feeding less than usual, has fewer wet nappies, is repeatedly vomiting, has ongoing diarrhoea or you are concerned about their hydration. Signs of dehydration can include fewer wet nappies, a dry mouth, fewer tears, sunken eyes or a sunken fontanelle. A baby who is unusually sleepy, difficult to wake, breathing rapidly or appears seriously unwell needs urgent medical assessment (NHS, 2024; NICE, 2009).

Different healthcare professionals have different roles in supporting infant feeding and assessing concerns. For more information, see What is an IBCLC? Feeding Support Explained and What does an infant feeding specialist do?.

Water guidance by age and feeding method

The table below summarises the guidance on offering water during the first year, according to age and feeding method.

| Age and feeding method | Water guidance | |---|---| | Under six months – exclusively breastfed | No additional water. Offer extra breastfeeds in hot weather. | | Under six months – combination-fed | Continue usual breast milk and formula feeds. Offer the breast more frequently if needed. No routine additional water. | | Under six months – exclusively expressed breast milk | Offer additional expressed breast milk if needed; express more frequently to provide it. | | Under six months – formula-fed | Continue usual formula feeds. A few small sips of cooled, boiled water may be offered between feeds during particularly hot weather. | | From around six months, once solids have started | Offer small sips of water from an open or free-flow cup with meals. Continue breast milk or first infant formula as the main drink. |

Adapted from Lucy Webber, IBCLC (2024), infographic on water intake in infancy.

References

First Steps Nutrition Trust (2024) FAQ: What are the recommendations for giving water during infancy? June 2024.

First Steps Nutrition Trust (2026) ‘Advice on drinks during hot weather, for families with babies and young children’, August 2026.

Kent, J.C., Prime, D.K. and Garbin, C.P. (2012) ‘Principles for maintaining or increasing breast milk production’, Journal of Obstetric, Gynecologic & Neonatal Nursing, 41(1), pp. 114–121. doi: 10.1111/j.1552-6909.2011.01313.x.

National Institute for Health and Care Excellence (NICE) (2009) Diarrhoea and vomiting caused by gastroenteritis in under 5s: diagnosis and management. Clinical guideline CG84.

National Institute for Health and Care Excellence (NICE) (2017) Constipation in children and young people: diagnosis and management. Clinical guideline CG99.

NHS (2021) Drinks and cups for babies and young children.

NHS (2023) How to make up baby formula.

NHS (2024) Dehydration.

Scientific Advisory Committee on Nutrition (SACN) (2018) Feeding in the first year of life. London: Public Health England.

World Health Organization (WHO) (2024) Breastfeeding: questions and answers. 2 October 2024.