Quick answer: Breastfed babies don’t need water before 6 months — breast milk is over 87% water and provides all the fluid they need. Formula-fed babies also generally don’t need extra water before 6 months, though small amounts can be offered in hot weather. From 6 months when solid foods begin, water with meals is appropriate and encouraged.
Why water before 6 months is not recommended
Breast milk is 87% water and adjusts its composition in real time — the first milk of a feed (foremilk) is higher in water content, essentially quenching thirst before the hindmilk provides calories and fat. Giving water to a breastfed baby before 6 months displaces breast milk from the feed, potentially reducing caloric intake. More critically, water given in large amounts to newborns and young infants can cause water intoxication (hyponatraemia) — diluting sodium levels to dangerous concentrations. This is rare but has caused serious illness and death. A young baby’s kidneys cannot process large water loads. The WHO recommendation of exclusive breastfeeding for 6 months explicitly includes no water.
Formula feeding and water
Formula-fed babies also generally don’t need supplemental water before 6 months — formula provides adequate fluid when prepared correctly at the right volume. In hot weather (above 30°C / 86°F) or if a formula-fed baby is clearly thirsty between feeds, small amounts of cooled boiled water (up to 2–3oz) can be offered. Don’t add extra water to formula — this dilutes the nutritional concentration in a way that matters for a small baby.
From 6 months: introducing water properly
When solid foods begin, water becomes important — fibre from vegetables and fruits requires additional fluid for healthy gut function, and babies eating solids need the additional hydration. Offer water in a small open cup, straw cup, or lidded cup at mealtimes. The amount needed is relatively small (2–4oz per meal is plenty initially, increasing as solids intake grows). Don’t fill babies up on water before meals — offer it during and after eating. Water should be cooled boiled water until 12 months in the UK; commercially bottled water or tap water is fine in the US after 6 months.
Drinks to avoid
Avoid for the entire first year: fruit juice (even diluted — high sugar, no nutritional advantage over whole fruit); sweetened drinks; flavoured water; cordials and squash; adult fruit juices; and herbal teas. Fruit juice, in particular, is associated with dental caries and provides empty calories that displace nutritionally superior foods. Even 100% orange juice provides sugar without the fibre of whole fruit.
Frequently Asked Questions
Can I offer water to help with constipation?
For formula-fed babies over 6 months who are constipated, small amounts of water between feeds can help. For breastfed babies under 6 months, constipation is unusual (and if it occurs, warrants medical evaluation rather than water supplementation). For babies over 6 months on solids, water with meals is the appropriate approach.
My formula-fed baby seems thirsty in summer — what should I offer?
Small amounts of cooled boiled water between formula feeds is appropriate in hot weather for formula-fed babies from any age. Signs of adequate hydration: pale yellow urine (not dark), at least 6 wet diapers per day, and no unusual thirst behaviour.
When can babies have tap water?
In the UK, tap water for babies should be boiled and cooled until 12 months to reduce bacterial risk. In the US, tap water safety standards generally allow use after 6 months without boiling, though many paediatricians still recommend boiling until 12 months for immunocompromised babies. Commercially bottled water can be used for babies over 6 months if tap water quality is a concern.
Related Reading
- 6 month old baby: starting solids – a complete first-foods guide
- Baby-led weaning recipes: 20 finger foods for 6-9 months
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