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, and giving water earlier poses real health risks. Once your baby reaches 6 months and begins eating solid foods, 4 to 8 ounces of water per day is the recommended range.
Why No Water Before 6 Months
A newborn’s stomach is tiny. At one month old, it’s roughly the size of an egg. Every sip of water takes up space that should go to breast milk or formula, which contain the calories, vitamins, minerals, and proteins your baby needs to grow. Water has none of those things. Giving it too early dilutes your baby’s calorie intake during a period when steady weight gain is one of the most important markers of health.
The risk goes beyond missed calories. Before 6 months, a baby’s kidneys are still immature and cannot efficiently process extra water. When an infant takes in too much water relative to their body size, sodium levels in the blood can drop dangerously low, a condition called water intoxication. It doesn’t take much. A rapid increase of just 7% to 8% in total body water can trigger symptoms. The sodium drop causes cells in the brain to swell, which can lead to irritability, extreme drowsiness, low body temperature, and in serious cases, seizures.
This is also why you should never add extra water when mixing powdered formula. Always measure the water first, then add powder, following the exact ratio on the container. Too much water means the formula won’t meet your baby’s nutritional needs. Too little water forces the kidneys and digestive system to work harder than they should.
How Much Water From 6 to 12 Months
Between 6 and 12 months, your baby can have 4 to 8 ounces (roughly half a cup to one cup) of water per day. This isn’t meant to replace breast milk or formula. It’s a small supplement that helps your baby get used to drinking water, supports digestion as solid foods enter the picture, and keeps things moving through the gut.
You don’t need to hit that range every day, especially at first. A few sips with meals is a fine starting point. The goal is gradual exposure rather than a strict daily quota. Breast milk or formula should remain the primary source of nutrition and hydration throughout the first year.
Choosing the Right Cup
Six months is also a good time to introduce a cup. Open cups and straw cups are the best options because they help your baby develop the oral muscles used for swallowing and eventually for speech. Sippy cups with hard spouts are not recommended because they can interfere with that development.
To start with an open cup, use a very small cup filled at least halfway. With your baby sitting upright in a high chair, bring the cup to their lips, tip it slightly, then take it away after a couple of seconds. They’ll dribble most of it at first, and that’s normal. Once your baby can manage a few swallows from an open cup, you can introduce a straw cup. If they can’t figure out the straw right away, trapping a small amount of water in the straw with your finger and releasing it into their mouth teaches them how suction works.
Water During Illness
If your baby between 6 and 12 months gets sick with vomiting or diarrhea, water alone is not the right fluid to offer. Plain water lacks the salts and sugars that help the intestines absorb fluid quickly. Instead, continue offering breast milk or formula. If your baby can’t keep that down, switch to a pediatric rehydrating solution that contains electrolytes. Give small amounts, about 2 teaspoons every 5 minutes, over two to four hours rather than large volumes at once.
After age 1, the guidance shifts. Diluted apple juice (half juice, half water) becomes an option for rehydration during stomach bugs, with about 3 teaspoons given every 5 minutes.
Signs of Water Intoxication
Water intoxication is rare when you follow the guidelines above, but knowing the warning signs matters. Watch for:
- Unusual fussiness that doesn’t match hunger, tiredness, or other obvious causes
- Extreme drowsiness or difficulty waking your baby
- Low body temperature (below 97°F)
- Puffiness or swelling in the face
- Unusually pale or clear urine with more wet diapers than normal (consistently more than 6 to 8 per day)
- Seizures
These symptoms reflect a dangerous drop in blood sodium. If you notice swelling, extreme drowsiness, or seizures, that’s a medical emergency.
Safe Water for Formula and Drinking
Whether you’re mixing formula or offering your 6-month-old their first sips, the water itself needs to be safe. Most tap water in the U.S. is fine to use, filtered or unfiltered. If you’re unsure about your local supply, contact your health department or use bottled water.
For babies younger than 2 months, premature babies, or infants with weakened immune systems, boil water for formula preparation and let it cool for about five minutes before mixing. The formula will still be too hot to feed right away, so wait until it reaches a comfortable temperature. During water advisories or emergencies, use bottled water or ready-to-feed liquid formula until authorities confirm the tap water is safe. Boiling does not remove chemical contaminants, so in those situations bottled water is the only reliable option.