Water for Babies: When to Introduce It, How Much Is Needed, and Using a Cup

Water for babies is a surprisingly nuanced topic — with guidelines that differ depending on whether your baby is breastfed, formula-fed, or weaning, and that change significantly around the six-month mark. Getting this right matters, because giving too much water to a young baby carries genuine risks, while too little can be an issue during weaning.

Before Six Months: Breastfed Babies

The NHS and World Health Organisation both recommend exclusive breastfeeding for the first six months of life. During this period, breastfed babies do not need water — even in hot weather.

Breast milk is approximately 87 per cent water, and its composition adapts to the baby's needs. In hot weather, the milk produced at the start of a feed (foremilk) is thinner and more watery, providing extra hydration. Offering water to an exclusively breastfed baby before six months is not recommended because:

• It can interfere with milk supply (a baby who fills up on water feeds less at the breast, reducing demand and therefore production)
• It can cause hyponatraemia (low sodium) — water intoxication — if given in large quantities, because a young baby's kidneys cannot excrete excess water efficiently. This is rare but serious.

If you are worried about dehydration in a breastfed baby during hot weather, the appropriate response is to offer more frequent breastfeeds, not water.

Before Six Months: Formula-Fed Babies

Formula-fed babies also generally do not need additional water, since formula made with the correct water-to-powder ratio provides adequate hydration.

However, in very hot weather, the NHS acknowledges that formula-fed babies can be offered a small amount of cool, boiled water between feeds. This should be plain, previously boiled tap water that has been cooled — not bottled still water (which may have high mineral levels) and not sparkling water. The amount is small — a few teaspoons to a few sips — to help with comfort rather than as a main hydration source.

This slight difference between breastfed and formula-fed guidance exists because formula is a fixed composition, whereas breast milk is adaptive. In practice, most formula-fed babies in a UK climate do not need extra water — this is mainly relevant during heat waves.

From Six Months: Introducing Water With Weaning

When solid foods are introduced from around six months, small amounts of water with meals become appropriate for all babies — breastfed or formula-fed. This serves two purposes:

1. It helps babies begin to develop cup-drinking skills (important for eventually dropping bottles)
2. As food is introduced, particularly starchy and protein-rich foods, a small amount of water supports digestion and helps prevent constipation, which is common in early weaning

The volume does not need to be large — a few sips with each meal is appropriate initially. Amounts increase naturally as babies become more established with solids.

How Much Water Does a Baby Need?

Between six months and twelve months, babies still get the majority of their fluids from breast milk or formula. The NHS suggests that formula-fed babies between six and twelve months need approximately 500–600 ml of formula per day (continuing to adjust as solids intake increases). Breastfed babies continue to feed on demand.

Formal water intake recommendations for babies are not as clearly quantified as those for older children and adults. The general guidance is that water should be available with meals and offered freely, but babies at this stage are not expected to drink significant quantities.

After twelve months, if full-fat cow's milk is introduced as a main drink (in a cup), water remains the other appropriate drink. Fruit juice should be avoided as a regular drink and, if given at all, should be well diluted and limited to mealtimes.

Introducing a Cup

The NHS recommends introducing a cup from six months of age — the start of weaning is a natural and ideal time to do this. Open cups and free-flow cups (without a non-return valve) are preferred over spout cups with valves, because they involve swallowing patterns more like normal drinking and are better for dental health.

Open cups for babies can seem messy initially, but babies adapt quickly and the skill develops over weeks of practice. Silicone-sided cups and small-handled training cups are available that help babies grip at this stage.

Doidy cups — angled open cups — are popular in Montessori-influenced and speech-and-language-recommended approaches, as they require less backward head tilting and are easier for babies to use.

Aim to phase out bottles by twelve months and have the baby drinking all fluids from a cup by this age, to protect dental health and reduce feeding difficulties later.

What About Boiled Water?

Tap water for babies over six months does not need to be boiled before drinking (unless there is an advisory in your area — these are very rare in the UK). Boiling and cooling water is the standard method for formula preparation under twelve months, but for a baby over six months being offered a cup of water with meals, room temperature tap water is fine.

Filtered tap water (through a standard jug filter) is acceptable but does not need to be specially treated.

What Not to Give

• Fruit juice — not recommended as a regular drink before twelve months, or at all in a bottle. Well-diluted juice (one part juice to ten parts water) can be offered occasionally in an open cup at mealtimes from six months, but is not nutritionally necessary.
• Squash, flavoured water, or sweetened drinks — not appropriate at any age in infancy.
• Sparkling water — not appropriate for babies and young children (high mineral content in some brands; no benefit).
• Herbal teas — generally not recommended for babies without specific clinical guidance.

Clean, plain water and breast milk or formula is genuinely everything a baby under twelve months needs to drink.