Under 6 Months — No Water Needed (and Why It Matters)
This is the single most important thing in this entire guide: babies under 6 months who are exclusively breastfed or formula-fed do not need water. Not in summer. Not when they seem thirsty. Not to help with wind or constipation.
Breast milk is approximately 87% water. Formula is similarly water-based. Both deliver hydration alongside electrolytes — sodium, potassium, chloride — in precisely the balance that infant kidneys can handle. This is what isotonic means: the fluid matches the body's own concentration, so the kidneys don't have to work to correct it.
Plain water doesn't have this balance.
Why Water Can Be Dangerous Under 6 Months
A young baby's kidneys are immature. They can process a certain volume of fluid per unit of time, but they cannot concentrate urine as efficiently as adult kidneys, and they cannot excrete excess water quickly.
When a young infant drinks plain water, the water dilutes the blood — specifically, it reduces blood sodium concentration. This condition is called hyponatraemia (low blood sodium). Sodium is the electrolyte that regulates fluid balance between cells and blood. When it falls too low, fluid moves into cells — including brain cells.
| Stage | What Happens |
|---|---|
| Baby drinks plain water | Water enters the bloodstream; no accompanying electrolytes to maintain blood sodium concentration |
| Kidneys cannot excrete fast enough | The immature infant kidney cannot remove the excess water quickly; the water accumulates in the blood |
| Blood sodium falls (hyponatraemia) | The excess water dilutes blood sodium; sodium falls below the level needed for normal cell function |
| Fluid shifts into cells | Low blood sodium causes fluid to move into cells by osmosis; this includes brain cells |
| Symptoms appear | Lethargy; irritability; poor feeding; in severe cases — seizures and loss of consciousness. The threshold is low: it does not take a large volume of water to cause this in a young infant. |
What About Formula Preparation?
Formula must be prepared with freshly boiled water cooled to no lower than 70°C. This is to kill bacteria in the formula powder — not because the water itself is unsafe. The water, once incorporated into the formula, delivers hydration alongside the electrolytes and nutrients in the formula. This is correct and safe. Drinking plain water in addition is not.
From 6 Months — Introducing Water the Right Way
When solid food is introduced — at around 6 months — water becomes appropriate alongside it. The purpose at this stage is partly hydration, and partly learning: the baby is beginning to develop the oral motor skills for cup drinking, and water is the right drink to practise with.
Open Cup — Not a Sippy Cup
The NHS and dental health organisations recommend introducing water from a free-flow cup (with no valve) or an open cup from 6 months. A valve-sealed sippy cup is not recommended.
| Cup Type | How the Child Drinks | Effect |
|---|---|---|
| Open cup or free-flow cup (no valve) | Child tips the cup; liquid flows naturally; child must use lips, tongue, and jaw coordination to drink | Develops the oral motor skills needed for normal drinking; liquid drains from the mouth and doesn't pool against teeth; messy but developmentally appropriate |
| Valve-sealed sippy cup | Child must bite or suck the valve to release liquid — the same negative-pressure suction used with a bottle or breast | Does not develop cup-drinking skills; pools liquid (including milk in some cases) against the upper front teeth, creating dental caries risk; delays the transition from bottle mechanics to open-cup drinking |
How Much Water from 6 Months?
At 6–12 months, breast milk or formula remains the primary fluid — water is additional and offered in small amounts at mealtimes. There is no specific volume target for water at this stage. Offer sips with meals; don't force; don't be concerned if the baby initially takes very little — the milk feeds are still providing most of the hydration.
From 12 months, whole cow's milk and water become the two main drinks. The target is approximately 300–400ml of whole milk per day, with water offered freely throughout the day.
UK Tap Water — No Need to Boil After 6 Months
UK tap water does not need to be boiled before being given to drink from 6 months. The UK's public water supply meets safety standards and is appropriate for drinking from 6 months onwards without boiling or filtering. If you are travelling outside the UK, follow local guidance for the destination.
Drinks by Age — What to Offer and What to Avoid
| Drink | Under 6 months | 6–12 months | 12 months–3 years |
|---|---|---|---|
| Breast milk | ✅ Complete hydration and nutrition | ✅ Remains primary fluid alongside solid food introduction | ✅ Can continue for as long as both parent and child wish |
| Formula milk | ✅ Complete hydration and nutrition if not breastfeeding | ✅ Remains primary fluid alongside solid food introduction | Whole cow's milk replaces formula as the main drink from 12 months; formula no longer nutritionally necessary |
| Plain tap water | ❌ Not appropriate — risk of water intoxication and hyponatraemia | ✅ Sips with meals in an open cup; UK tap water safe without boiling | ✅ Main drink alongside milk; offer freely throughout the day |
| Whole cow's milk (as drink) | ❌ Not appropriate as a drink — displaces milk feeds, lower in iron than breast milk/formula | ❌ Not as main drink; fine as ingredient in cooking from 6 months | ✅ 300–400ml per day; full-fat whole milk until 2 years; do not switch to semi-skimmed before 2 years |
| Fruit juice (any type) | ❌ | ❌ NHS recommends no juice before 12 months — dental acid erosion, sugar, displaces milk | ⚠️ Not nutritionally necessary; if given: maximum 100–150ml per day, diluted approximately 1:10, at mealtimes only, from an open cup — never in a bottle |
| Squash, cordial, sweetened drinks | ❌ | ❌ | ❌ No squash, cordial, or sweetened drinks at any point in this period — dental erosion, sugar or sweetener habituation, displacement of nutritious drinks |
| Fizzy drinks | ❌ | ❌ | ❌ Dental erosion; gas; no nutritional value; no fizzy drinks before 5 years at minimum |
| Tea (including herbal tea) | ❌ | ❌ | ❌ Tannins in regular tea inhibit non-haem iron absorption by up to 60% — particularly harmful at an age when iron intake from food is critical; caffeinated tea is inappropriate; herbal teas are not recommended for toddlers |
| Fortified soya milk (unsweetened) | ❌ | ❌ as main drink | ✅ Suitable as main milk drink for plant-based families from 12 months; must be fortified with calcium, iodine, and vitamin D; unsweetened |
| Oat, almond, rice, coconut milk | ❌ | ❌ as main drink; fine in cooking | ⚠️ Not recommended as main milk drink — lower protein and calcium than cow's milk or fortified soya; rice drinks specifically contain inorganic arsenic (FSA recommends avoiding under 5 years as a drink); can be used in cooking |
Why Fruit Juice Is Not a Good Hydration Choice
This is one of the most commonly misunderstood areas of infant and toddler nutrition. Fruit juice feels healthy — it comes from fruit. But for young children, it carries specific risks regardless of whether it is fresh-squeezed, organic, or packaged.
- Dental acid erosion: fruit juice has the same pH and acid profile whether fresh-squeezed or packaged; it erodes tooth enamel on contact; once teeth appear (usually from around 6 months) they are immediately at risk from acidic drinks — diluting juice reduces the volume of acid but does not remove it
- Sugar: fruit juice concentrates fruit sugars in a form that takes seconds to consume and provides no fibre; the same sugars consumed as whole fruit come with fibre that slows absorption and provides satiety
- Displacement: juice is filling without being nutritious relative to breast milk, formula, or whole fruit; it displaces the drinks and foods that actually build the diet
- Preference programming: sweet drink consumption in infancy and toddlerhood is associated with ongoing preference for sweet drinks through childhood
Signs of Dehydration — What to Watch For
Most of the time, a well-fed baby is a well-hydrated baby. Dehydration in an exclusively breastfed or formula-fed baby is uncommon when feeding is going well. But it can happen — most commonly during illness (vomiting or diarrhoea), in very hot weather, or if feeding frequency has significantly reduced.
The most reliable single indicator is wet nappies.
- Day 1–2 (newborn): 1–2 wet nappies — normal; colostrum volume is small
- Day 3–4: 3–4 wet nappies as milk comes in or formula volume increases
- Day 5 onwards: 6 or more wet nappies per 24 hours — consistently
- Urine colour: pale yellow or colourless = well hydrated; dark yellow or amber = increase feeds; orange-tinged = contact health visitor or GP
- Tip: modern disposable nappies are highly absorbent; if you are unsure whether a nappy is wet, place a small piece of tissue inside before putting the nappy on — the tissue will clearly show any wetness
| Signs | What to Do |
|---|---|
| Mild dehydration — monitor and respond | |
| Fewer wet nappies than usual (still above 4 per day from day 5) | Offer more breastfeeds or formula feeds; for babies 6 months+, offer sips of water; monitor closely |
| Slightly darker yellow urine | Increase feed frequency; offer water for 6 months+ alongside milk feeds |
| Dry or sticky lips | Offer a feed; offer water sips for 6 months+; monitor wet nappies over the next few hours |
| Fewer or no tears when crying (in babies over 2 months) | Offer a feed; if this persists alongside reduced wet nappies, contact health visitor |
| Less active than usual; quieter than usual | Offer a feed; monitor alongside other signs; if combined with other mild signs, contact health visitor |
| Concerning — contact GP or NHS 111 | |
| Fewer than 4 wet nappies in 24 hours from day 5 | Contact health visitor or GP; intake is insufficient |
| No wet nappy for 8 or more hours | Contact GP or NHS 111 promptly |
| Sunken fontanelle (the soft spot on top of the head appears sunken or concave) | Contact GP or NHS 111 promptly — sunken fontanelle indicates significant dehydration |
| Sunken eyes; dry mouth and tongue; no saliva | Contact GP or NHS 111 promptly |
| Baby is unusually limp, difficult to rouse, or very lethargic | Seek urgent medical attention — call 999 or go to A&E if the baby is very unresponsive |
| Cold, blotchy, or mottled skin alongside dehydration signs | Seek urgent medical attention |
Hot Weather Hydration — By Age
UK summers can bring prolonged warm periods that raise valid hydration concerns, particularly for parents of young babies. The guidance is simple but different depending on the baby's age.
Under 6 months in hot weather
Offer more breastfeeds or formula feeds —
not water. Breast milk composition shifts
in hot weather to provide more watery
foremilk; the body adjusts. Formula provides
the correct fluid and electrolyte balance.
Practical steps: keep the room cool (16–20°C
if possible); use a fan to circulate air (not
directed at the baby); dress the baby in
lightweight breathable clothing; use shade
outdoors; avoid direct sun especially between
11am and 3pm.
The answer to "it's hot, should I give
water?" for a baby under 6 months is always:
offer a breastfeed or a formula feed.
6–12 months in hot weather
Continue to offer breastfeeds or formula
feeds as the primary fluid. Additionally,
offer small sips of water more frequently
throughout the day from an open cup —
particularly with meals and snacks.
Keep the baby in shade; apply a hat when
outdoors; avoid direct sun in peak hours;
ensure the room at night is kept cool.
Watch wet nappies — this is the most
reliable indicator of adequate hydration.
Six or more wet nappies per day means
intake is adequate.
Toddlers in hot weather
Offer water more frequently throughout the
day — before, during, and after outdoor
activity. Whole milk counts toward fluid
intake and should continue at usual volumes.
Toddlers often do not register thirst as
reliably as older children and adults — offer
water without waiting for the child to ask
for it. A water bottle available throughout
the day makes this easy.
Pale urine and normal wet nappies/toilet
visits are the indicators of adequate hydration.
If urine is consistently dark yellow, increase
water intake.
Hydration During Illness — Vomiting and Diarrhoea
Vomiting and diarrhoea are the most common causes of dehydration in young children. The approach differs by age.
| Age | Primary Response | When to Contact GP / NHS 111 |
|---|---|---|
| Under 6 months | Continue breastfeeding or formula feeding — these provide fluid and electrolytes. Do not give plain water or oral rehydration solution without medical advice. If the baby is vomiting after every feed or has significant diarrhoea, contact your GP or NHS 111 promptly — dehydration can develop quickly in young infants. | Any vomiting in a baby under 3 months; significant vomiting (after every feed) in a baby under 6 months; any signs of dehydration; temperature above 38°C in under 3 months or 39°C in 3–6 months; if you are concerned at any point |
| 6–12 months | Continue breastfeeding or formula feeding. Offer small, frequent sips of water between feeds. For significant vomiting or diarrhoea, a GP or health visitor may recommend an oral rehydration solution (ORS such as Dioralyte) — these replace the sodium and potassium lost in diarrhoea and vomiting; give ORS only on medical advice at this age. | No wet nappy for 8+ hours; signs of dehydration (sunken fontanelle, sunken eyes, unusual lethargy); vomiting that prevents any fluid being retained; diarrhoea for more than 24 hours; blood in stool or vomit; temperature above 39°C |
| 12 months – 3 years | Continue milk feeds; offer frequent small sips of water; ORS (Dioralyte) may be recommended by GP for significant gastroenteritis — it replaces electrolytes more effectively than plain water. Continue offering food if the toddler shows any interest — solid food can be resumed as soon as tolerated; do not withhold food for 24 hours as previously advised. | Signs of dehydration; no urine for 8+ hours; vomiting for more than 24 hours; diarrhoea for more than 7 days; blood in stool; the child appears very unwell, unusually drowsy, or has a high temperature that is not responding to paracetamol |
How Food Contributes to Hydration — From 6 Months
From the moment solid food is introduced, food becomes a source of water alongside drinks. Many parents don't realise how significant this contribution is.
| Food Category | Approximate Water Content | Practical Implication |
|---|---|---|
| Vegetables (courgette, broccoli, cucumber, tomato) | 85–96% water | A serving of cooked vegetables contributes meaningfully to daily fluid intake; important in hot weather |
| Fruit (watermelon, strawberries, melon, pear) | 85–95% water | Fruit at meals and snacks contributes significant fluid alongside fibre, vitamins, and natural sugars |
| Pureed or mashed food with milk or water added | Depends on preparation; typically 70–85% water | Baby purées are largely water; they count toward fluid intake, which is why young babies on solids don't need large additional water volumes |
| Porridge (made with water or milk) | 80–85% water | A bowl of porridge made with milk provides hydration, calcium, and energy simultaneously |
| Yoghurt | 75–85% water | Full-fat plain yoghurt as a snack or meal component contributes both hydration and calcium |
| Bread, pasta, rice, potato | 30–80% water (cooked) | Cooked starchy foods contribute less water than fruit and vegetables but still add to total fluid intake |
This is part of why the water volume needed from drinks is lower than parents often expect — a baby or toddler eating well from a varied diet is receiving significant fluid from food throughout the day.
Quick Reference — Hydration Checklist by Age
Under 6 months
✓ Breastfeed or formula feed on demand
✓ In hot weather: more breastfeeds or formula, not water
✓ Check: 6+ wet nappies per day from day 5
✓ Check: pale yellow urine
✗ No plain water
✗ No juice, squash, or any other drinks
✗ No diluted formula
6–12 months
✓ Breast or formula feeds remain the primary fluid
✓ Sips of plain water with meals — open cup
✓ UK tap water safe without boiling
✓ Check: 6+ wet nappies per day; pale urine
✗ No juice
✗ No squash or sweetened drinks
✗ No cow's milk as main drink
✗ No valve sippy cups
12 months – 3 years
✓ Whole cow's milk 300–400ml per day (full-fat)
✓ Plain water offered freely throughout the day
✓ Water bottle available during the day
✓ Check: pale urine; normal toilet/nappy output
✗ No juice before 12 months; minimal and diluted after
✗ No squash, cordial, sweetened drinks
✗ No tea (inhibits iron absorption)
✗ No fizzy drinks
✗ No low-fat milk before 2 years
Frequently Asked Questions
No — babies under 6 months should not have water. Breast milk and formula provide complete hydration including the correct electrolyte balance for immature infant kidneys. Plain water lacks electrolytes; given to a young infant, it dilutes blood sodium (hyponatraemia), which the kidneys cannot correct quickly enough. Even small amounts can cause water intoxication in a young baby. In hot weather, offer more breastfeeds or formula feeds instead.
From around 6 months, when solid food is introduced. Offer sips of plain water with meals in a free-flow open cup. UK tap water is safe without boiling from 6 months. At this age, water is an addition to milk feeds — not a replacement. Breast milk or formula remains the primary fluid throughout the first year.
Watch for: fewer wet nappies than usual; darker yellow urine (pale yellow or colourless = well hydrated); dry lips; fewer tears when crying (in babies over 2 months); unusual quietness or reduced activity. Contact your GP or NHS 111 if: no wet nappy for 8+ hours; sunken fontanelle (soft spot on top of the head looks dipped); sunken eyes; dry mouth; the baby is unusually limp or difficult to rouse.
Under 6 months: offer more breastfeeds or formula feeds — not water. Breast milk composition shifts in warm weather to provide more watery foremilk. Keep the baby cool, in shade, and out of direct sun between 11am and 3pm. From 6 months: offer sips of water more frequently alongside regular milk feeds. Check wet nappies — 6+ per day is the target.
No — the NHS recommends no fruit juice before 12 months. Fruit juice contains dental acids and sugars that erode tooth enamel (even from the first teeth) and displaces the more nutritious milk feeds. After 12 months, if offered: maximum 100–150ml per day, diluted approximately 1 part juice to 10 parts water, at mealtimes only, from an open cup — never in a bottle. Juice is not nutritionally necessary at any age.
Valve-sealed sippy cups require the same suction action as a bottle and don't develop the oral motor skills for normal cup drinking. They also pool liquid against the upper front teeth, creating a dental caries risk. A free-flow cup (no valve) or an open cup without a lid develops proper cup-drinking skills, is better for teeth, and is the NHS-recommended approach from 6 months.
For babies under 6 months: water should not be given to drink at all. For formula preparation, water must be boiled (to kill bacteria in the powder). From 6 months: UK tap water does not need to be boiled before being given to drink — the UK public water supply meets safety standards. If travelling outside the UK, follow local guidance.
Total fluid for a toddler (1–3 years) is approximately 1 to 1.3 litres per day — but this includes milk, water, and fluid from food. In practice: 300–400ml whole milk per day, plus plain water offered freely throughout the day. There is no need to measure — offer water at meals, snacks, and throughout the day; pale urine indicates adequate hydration.
Yes — completely. Breast milk is approximately 87% water and also contains the electrolytes (sodium, potassium, chloride) needed to maintain fluid balance. It is isotonic — meaning it matches the body's own fluid concentration so the kidneys don't have to correct it. In hot weather, the water content of early breast milk increases further. A fully breastfed baby under 6 months needs nothing else for hydration.
Log feeds, nappies, and milestones
so hydration patterns are easy to spot.
Lunara lets you log feeds and nappy output alongside growth and milestones — so you always know when the last feed was, whether wet nappies are on track, and how the day is going at a glance. Especially useful during growth spurts, hot weather, or illness, when patterns shift quickly. Free to start.