「Babies need extra water before 6 months」

Where the claim comes from

Adults drink water when thirsty, and more of it in hot weather, and that habit gets applied unchanged to small babies. Many families also feel a baby needs a little water between feeds to "rinse things through".

What the evidence says

The American Academy of Pediatrics (AAP) says healthy babies do not need extra water: breast milk or formula provides all the fluid they need. And extra water is not merely unnecessary. A CDC case report describes two infants under two months old in 1993 who were given bottled water for several days and were admitted with seizures from low blood sodium (both recovered fully); a ten-year review at the same hospital found 27 more cases of low-sodium seizures in infants under 1 year, all from too much plain water. The report explains that babies under 6 months have immature kidneys, so excess water dilutes the sodium in their blood, and concludes that parents should be discouraged from giving water — tap or bottled — as a supplement to infants under 6 months.

What to do instead

• Under 6 months, breast milk or formula is the only drink.
• In very hot weather a small amount of water may be needed — ask the doctor how much before giving any.
• Once solids start, a little water in a cup is fine: the CDC suggests 4 to 8 ounces (about 120–240 ml) a day from 6 to 12 months, and the AAP caps it at 1 cup (8 ounces) a day.
• For vomiting or diarrhoea, use oral rehydration solution rather than plain water.