Babies can start drinking small amounts of water at 6 months old. Before that age, breast milk or formula provides all the hydration an infant needs, even in hot weather. Between 6 and 12 months, the recommended amount is 4 to 8 ounces per day, which works out to about half a cup to one cup.
Why Babies Under 6 Months Shouldn’t Have Water
A newborn’s kidneys are too immature to process extra water efficiently. Giving water to a young infant can fill their tiny stomach, leaving less room for breast milk or formula, which are their only sources of calories and nutrients. Even a few ounces of water can displace a meaningful portion of a feeding at that age.
The more serious risk is water intoxication, a condition where excess water dilutes the sodium in a baby’s blood. When sodium drops rapidly, it causes cells in the brain to swell. Symptoms include unusual irritability or sleepiness, low body temperature, puffiness, and in severe cases, seizures. Infants are especially vulnerable because their bodies are small and their kidneys can’t flush excess water the way an adult’s can.
This same risk applies to formula preparation. Adding too much water when mixing powdered formula dilutes the nutrients and can push a baby toward water intoxication or poor weight gain over time. Always follow the exact water-to-powder ratio on the label.
What About Hot Weather?
Parents often worry about dehydration during summer, but the advice holds: no water before 6 months, even on the hottest days. Breast milk and formula already contain plenty of water. If your baby seems thirsty, offer an extra feeding instead.
To keep a young infant cool, dress them in breathable cotton, skip blankets, and stay in the shade. A handheld misting fan can help too. Watch for signs of dehydration like fewer wet diapers, darker urine, or constipation. If those appear, increasing breast milk or formula feedings is the right first step.
How Much Water From 6 to 12 Months
Once your baby reaches 6 months and starts eating solid foods, you can introduce water. The CDC and AAP both recommend 4 to 8 ounces per day during this stage. That’s a small amount on purpose. Breast milk or formula should still be the primary source of nutrition and hydration through the first birthday. The goal with water at this age is to let your baby practice drinking and get used to the taste, not to replace milk feedings.
A good approach is to offer breast milk or formula first, then give a few sips of water with meals or snacks. This keeps milk intake on track while letting your baby explore water in small amounts.
Choosing the Right Cup
Six months is also when most babies are developmentally ready to try a cup. Look for signs like sitting up independently, holding objects with both hands, and bringing things to their mouth. At that point, you can start offering water in a cup rather than a bottle.
An open cup with no lid is the best option for oral development. It teaches babies to sip rather than suck, which supports healthy tongue movement and jaw growth. If spills are a concern, a two-handled training cup with a snap-on lid (but no valve) is a reasonable middle ground. The American Dental Association specifically recommends avoiding spill-proof cups like 360-degree lids or cups with valves, because they encourage a sucking motion similar to a bottle. Sippy cups with hard spouts have the same issue and can restrict tongue movement if used frequently. If you do use one, treat it as a short-term bridge to an open cup.
What Type of Water Is Safest
Tap water is fine for most babies, but boiling it first adds an extra layer of safety by killing bacteria and viruses that may be present. Bring the water to a full rolling boil for at least one minute, then let it cool to roughly body temperature before offering it. This applies to bottled water too. While bottled water is generally safe for adults, it isn’t necessarily sterile enough for infants.
If your home uses well water, avoid giving it to your baby unless you’ve had it tested recently. Untested well water can contain bacteria or high mineral levels. Low-fluoride bottled water (labeled “purified,” “distilled,” or “deionized”) is a safer substitute.
Fluoride in tap water is beneficial for dental health, but some parents worry about excess fluoride for very young children. If that’s a concern, you can alternate between regular tap water and low-fluoride bottled water. Ready-to-feed liquid formula is another option, since it contains less fluoride than formula mixed with tap water.
After the First Birthday
Once your child turns 1, water becomes a regular part of their diet alongside whole milk. At this stage, their kidneys are mature enough to handle larger volumes, and solid foods make up a growing share of their calories. Most toddlers between 12 and 24 months do well with 1 to 4 cups of water per day, depending on their size, activity level, and how much milk they’re drinking. The transition from “sips with meals” to “water throughout the day” happens naturally as solid food intake increases and milk feedings taper off.