Babies can start drinking small amounts of water at around 6 months old, when they begin eating solid foods. Before that age, breast milk or formula provides all the hydration and nutrition an infant needs. Giving water too early can interfere with feeding and, in rare cases, cause serious health problems.
Why 6 Months Is the Guideline
The American Academy of Pediatrics recommends breastfeeding as the sole source of nutrition for about the first 6 months. Breast milk is roughly 80% water, so even in warm weather, a healthy baby who is feeding well stays hydrated without any extra fluids. Formula works the same way. Adding water before 6 months creates two problems: it fills your baby’s tiny stomach with zero-calorie liquid, and their kidneys aren’t mature enough to handle the extra load efficiently.
What Happens If a Young Baby Drinks Water
An infant’s kidneys are still developing and can’t flush out large amounts of water the way an adult’s can. When a baby takes in more water than their kidneys can process, sodium levels in the blood drop. This condition, called water intoxication, can cause irritability, drowsiness, swelling, and in severe cases, seizures. It’s uncommon, but the risk is real in babies under 6 months because it takes very little water to overwhelm their system.
Even without reaching that extreme, water displaces breast milk or formula in a baby’s diet. Because water has no calories, it creates a false sense of fullness. The baby nurses or bottle-feeds less, takes in fewer calories, and may lose weight or develop higher bilirubin levels (the substance that causes jaundice). Replacing nutrient-rich milk with water can also weaken the immune benefits that breast milk provides.
How Much Water From 6 to 12 Months
Once your baby starts solids around 6 months, you can offer 4 to 8 ounces of water per day, which is about half a cup to one cup. This isn’t meant to replace milk feeds. At this stage, the goal is to let your baby practice drinking and get familiar with the taste of water. Most of their hydration still comes from breast milk or formula.
Offer water in small sips alongside meals rather than as a standalone drink between feedings. If you live in an area with fluoridated tap water, these small sips also help protect emerging teeth from decay.
Water After the First Birthday
After 12 months, water becomes a more important part of your child’s daily fluid intake, especially as milk consumption decreases and solid food takes over. Toddlers weighing around 10 to 12 kg (22 to 26 pounds) generally need roughly 1,000 to 1,100 ml of total fluid per day, which includes water, milk, and the moisture in food. A practical target is offering water freely with meals and snacks and letting your toddler drink when thirsty.
By this age, water and plain milk should be the primary beverages. Juice, flavored milks, and sugary drinks aren’t necessary and can crowd out more nutritious options.
Choosing the Right Cup
The AAP suggests offering a cup when your baby starts solid foods, around 6 months. Open cups, straw cups, and sippy cups all work at first, but there’s a developmental advantage to open cups and straws. Many sippy cups have a valve that forces kids to suck, which mimics bottle-feeding and doesn’t help them learn new drinking skills.
Aim for your child to drink from an open cup by about age 2. Some families skip the sippy cup entirely and go straight from breast or bottle to a regular cup, which is perfectly fine.
What About Hot Weather or Constipation?
Parents often worry about dehydration during summer heat. For babies under 6 months, the answer is more frequent breast milk or formula feeds, not water. If your baby is producing a normal number of wet diapers, feeding well, and alert, they’re getting enough fluid.
For constipation, the Mayo Clinic notes that babies 1 month and older can try a small amount of water to help soften stools. This is a targeted remedy in small quantities, not routine daily water intake. Apple or pear juice in small amounts can also help because they contain sorbitol, a natural sugar that draws water into the intestines.
Signs Your Baby Might Be Dehydrated
Whether your baby is 2 months or 10 months old, watch for these signs that they need more fluids:
- Fewer wet diapers than usual
- Sunken soft spot on top of the head
- Sunken eyes or few tears when crying
- Unusual drowsiness or irritability
For babies under 6 months, the solution is more breast milk or formula. For babies over 6 months, you can offer water alongside increased milk feeds.
Tap Water, Bottled Water, and Fluoride
Fluoridated tap water is safe for mixing formula and for babies to drink once they’re 6 months old. The AAP, ADA, and CDC all agree that fluoride at recommended levels is effective for preventing tooth decay and has not been linked to lower IQ scores. There is a small cosmetic risk of faint white spots on teeth (fluorosis) when fluoridated water is used to mix formula before 6 months, but it’s not harmful. If that concerns you, use ready-to-feed formula or bottled water labeled fluoride-free.
Bottled water isn’t required to list its fluoride content on the label unless it makes a specific claim, so you may not know what you’re getting. If you use well water or have concerns about contaminants, check with your local health department about testing options.