Hydration for infants (0–12 months)
Under six months: breastmilk or formula only. After six months: small sips of water, introduced carefully.
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Infant hydration is the one age band where the rule book is completely different from everyone else in the household. Before 6 months of age, a healthy, full-term infant should get 100% of their fluids from breastmilk or formula — plain water is not only unnecessary but can be dangerous. Even small amounts of water displace the calories and electrolytes an infant needs, and in rare cases tip them into water intoxication. After 6 months, as solids start, a few sips of water from an open cup at mealtimes is appropriate — but milk (breast or formula) remains the dominant fluid source until 12 months. This page is for parents who want the right answers for their baby's exact month, plus the clearest version of the warning signs that mean you call the pediatrician today, not next week.
What pediatric guidelines actually say
0–6 months: no plain water
The American Academy of Pediatrics, NHS, and WHO all agree — breastmilk or formula provides 100% of the water a healthy infant needs in the first six months. Adding water risks hyponatremia (dilutional low sodium) and can reduce feeding volume.
Source: AAP infant feeding guidance
6–12 months: up to 4–8 oz (120–240 ml) of water per day, from a cup
Once solids start, small sips of water with meals are appropriate — typically 1–2 oz at a time. Breastmilk or formula still provides the majority of daily fluids; water is for practice and hygiene, not volume.
No fruit juice before 12 months
AAP guidance has tightened — no juice under 1 year, and even after 1 year limited to 4 oz/day. Juice spikes sugar intake without adding hydration benefit over plain water.
In hot weather or during illness, feed MORE breastmilk/formula — not more water
Fluid-replacement in infants is done by extra feeds, not by adding water. If baby is feverish, vomiting, or refusing to feed, contact your pediatrician the same day rather than improvising with water or juice.
What actually works day-to-day
- Track wet diapers, not ml — 5–6+ wet diapers/day is the reliable at-home hydration signal for an infant
- Pale straw urine, not clear and not dark yellow, is the target colour
- For the 6–12 month phase, offer water in a small open cup at meals — sippy cups are fine but open-cup practice starts now
- Never add water to reduce formula concentration — always mix formula exactly as the label directs
- Keep a small cup of water within reach at meals but don't force intake — the baby's appetite for milk is the signal
- On a hot day, offer the breast or bottle more frequently rather than adding plain water
- A pacifier is NOT a hydration tool — if baby seems thirsty, feed them
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Open the calculator →Signs to watch — some are emergencies
Signs of Dehydration
- Fewer than 4 wet diapers in 24 hours (call pediatrician same day)
- No wet diaper in 6+ hours in a baby under 3 months (emergency department)
- Sunken soft spot (fontanelle) — call 911 or go to ER
- No tears when crying, dry mouth, unusually sleepy or hard to rouse
- Refusing to feed for 4+ hours in a baby under 6 months
- Dark yellow or amber urine on more than one diaper in a row
- Vomiting or diarrhea that lasts >6 hours in an infant
When to Contact Your Healthcare Provider
- Any of the emergency signs above — same-day pediatrician call or ER visit, not 'wait and see'
- Vomiting or diarrhea in an infant under 6 months — call the same day
- Fever above 100.4°F (38°C) in an infant under 3 months — ER
- Persistent refusal to feed, unusual lethargy, or any sudden change in behaviour
- If you've been advised by anyone to 'just give water' to an infant under 6 months — please check with your pediatrician first
Frequently Asked Questions
Can a 4-month-old have a little water in hot weather?
No. The American Academy of Pediatrics is explicit that infants under 6 months should not be given plain water, even in hot weather. If you're worried about hydration in heat, offer the breast or bottle more often — that's the correct answer. Plain water in a small infant can cause hyponatremia (dangerously low sodium), which can lead to seizures.
How much water should my 9-month-old drink?
About 4–8 oz (120–240 ml) per day, offered in small sips from an open cup with meals. The majority of fluids should still come from breastmilk or formula. Don't worry if your 9-month-old only takes a sip or two of water — milk is still the main hydration at this age.
What are the signs my baby is dehydrated?
Fewer than 4 wet diapers in 24 hours, dry mouth, no tears when crying, sunken soft spot, or unusual sleepiness. Any one of these is a reason to call your pediatrician the same day. A sunken fontanelle or a baby who is hard to rouse is an emergency — go to the ER.
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