Babies can start having small sips of water at 6 months old. Before that age, breast milk or formula provides all the hydration an infant needs, and giving water earlier can actually be harmful. Both the American Academy of Pediatrics and the World Health Organization agree on this 6-month mark.
Why 6 Months Is the Threshold
For the first 6 months of life, breast milk or formula is a complete source of nutrition and hydration. Exclusive breastfeeding means no other food or drink, not even water, for that entire period. Formula-fed babies get their hydration the same way. A healthy baby’s fluid needs are fully covered by their milk intake alone, even in hot weather.
The 6-month guideline isn’t arbitrary. Before that age, a baby’s kidneys are still immature and can’t handle excess water efficiently. Giving water too early also fills up a tiny stomach, which means the baby drinks less milk and misses out on the calories and nutrients they need to grow.
The Risk of Water Before 6 Months
The most serious danger of giving a young baby water is a condition called water intoxication. When an infant takes in too much water relative to their body size, sodium levels in the blood drop rapidly. This disrupts normal cell function in the brain, causing irritability, excessive sleepiness, low body temperature, swelling, and in severe cases, seizures. Symptoms appear when total body water increases by as little as 7 to 8 percent, which doesn’t take much volume in a small infant.
Babies under 6 months are especially vulnerable for two reasons: their kidneys can’t excrete excess water as quickly as an older child’s, and their strong hunger drive means they’ll readily swallow whatever liquid is offered. Cases of hyponatremic seizures have been documented in infants fed plain water or overly diluted formula.
How Much Water From 6 to 12 Months
Once your baby turns 6 months and starts solid foods, you can offer 4 to 8 ounces of water per day. That’s roughly half a cup to one cup. This small amount won’t replace much breast milk or formula at this stage. Think of it as practice rather than a primary source of hydration.
You don’t need to stress about hitting a specific ounce target. Some babies take a few sips and push the cup away, and that’s fine. The goal is to let them get used to the taste and the mechanics of drinking from something other than a breast or bottle. Breast milk or formula should still be the main drink through the first year.
Choosing the Right Cup
When you introduce water, skip the bottle. This is a good opportunity to start practicing with an open cup (held by you) or a straw cup. Traditional sippy cups with spill-proof valves are popular but aren’t the best choice for oral development. An open cup helps babies learn to control the flow of liquid with their lips, which supports speech and swallowing skills over time.
At 6 months, you’ll hold the open cup and tip small sips into your baby’s mouth. Expect mess. By around 9 months, many babies can start using a straw cup with some independence. Either option is preferable to a spouted sippy cup.
Tap Water, Bottled Water, and Fluoride
Fluoridated tap water is safe for babies. Fluoride exposure during infancy helps prevent tooth decay, and in most cases regular tap water is perfectly fine for mixing formula or offering as a drink. One minor consideration: if your baby’s main food source is powdered or liquid concentrate formula mixed consistently with fluoridated water, there’s a small chance of developing fluorosis. This is a cosmetic issue (faint white lines on teeth), not a health risk.
If fluorosis concerns you, you can alternate between tap water and low-fluoride bottled water (labeled purified, demineralized, or distilled) when preparing formula. If you use only low-fluoride water, your baby’s doctor may recommend fluoride supplements starting at 6 months. For most families, standard tap water is the simplest and safest choice.
Are There Exceptions Before 6 Months?
In rare cases, a pediatrician may suggest a small amount of water for a baby younger than 6 months. Constipation is the most common reason. The Mayo Clinic notes that for babies 1 month and older who are constipated, a small amount of water or fruit juice may be added to the diet. This means a teaspoon or two, not ounces, and only on a doctor’s recommendation. It’s not something to try on your own.
Oral rehydration solutions are also an exception. If a baby has vomiting or diarrhea, a doctor may recommend a specific electrolyte solution to prevent dehydration. Plain water is not a substitute for this because it lacks the sodium and sugar needed to restore fluid balance.
How to Tell if Your Baby Is Getting Enough Fluids
Wet diapers are the most reliable everyday indicator. After the first week of life, a well-hydrated baby produces at least 6 wet diapers per day, with no more than 8 hours between them. If you’re ever unsure whether your baby is getting enough milk, diaper count is the simplest check.
Signs of dehydration to watch for include dry or cracked lips, no tears when crying, a sunken soft spot on top of the head, skin that feels less elastic than usual, excessive sleepiness, and extreme fussiness. Fast breathing or a rapid heart rate can also signal dehydration. In a baby under 6 months, the solution to dehydration is more breast milk or formula, not water.
Water After the First Birthday
Once your child turns 1, water becomes a bigger part of daily hydration. Most toddlers transition to whole milk and water as their primary drinks. At this point, you can offer water freely throughout the day, especially with meals and snacks. There’s no strict ounce limit for toddlers, but making water available in a cup they can access helps build a healthy drinking habit early. Juice, flavored milks, and sweetened drinks aren’t necessary and are best limited or avoided entirely in the first few years.