Newborns and infants under six months of age should not be given plain water. Breast milk or infant formula provides all the necessary fluid and nutrition a baby needs for healthy development. Introducing water too early can pose significant health risks. This guidance is based on the unique physiological needs of a developing infant.
The Immediate Safety Concern: Why Water is Not Recommended
Giving plain water to a baby before six months introduces a serious hazard known as water intoxication, a condition that results from an imbalance of electrolytes in the body. An infant’s kidneys are immature and significantly smaller than an adult’s, having a reduced capacity to filter and excrete excess water. When a baby consumes too much water, it rapidly dilutes the concentration of sodium in their bloodstream, a condition called hyponatremia.
Sodium is an electrolyte responsible for regulating fluid balance and nerve function. Its dilution can cause cells, particularly those in the brain, to swell. Symptoms of this dangerous imbalance can include lethargy, irritability, low body temperature, and in severe cases, seizures, coma, or permanent brain damage. This risk is heightened because an infant’s stomach is quite small—about the size of an egg at one month—and water quickly fills that space.
The other major concern is nutrient dilution, which occurs when water takes up room in the baby’s tiny stomach without providing any calories or nutrients. This displacement can reduce the baby’s overall intake of milk or formula, leading to insufficient calorie consumption and potentially hindering proper weight gain. Infants rely on milk for dense nutrition, and anything that interferes with that intake can result in poor growth or a failure to thrive. Even in hot weather, babies under six months should be offered more frequent milk feeds rather than water.
Understanding the Nutritional Role of Breast Milk and Formula
Newborns do not require additional water because their primary sources of nutrition are already largely composed of water. Breast milk, for example, is approximately 87% water, which is more than enough to satisfy an infant’s hydration needs. Similarly, infant formula, when prepared according to the manufacturer’s instructions, provides an appropriate balance of fluid and nutrients.
These specialized fluids are designed to be a complete food source, supplying a complex mix of fats, proteins, vitamins, and minerals that water simply lacks. The body’s system of fluid and electrolyte management is built to process the constituents of milk, which serve both to nourish and to hydrate. Offering water beyond what is used to mix powdered formula is unnecessary and disrupts this system.
The Timeline for Introducing Water
The consensus among pediatric health organizations is that water can be introduced when a baby reaches six months of age. This timing corresponds with the introduction of solid foods into the diet. By six months, a baby’s kidneys are more developed, allowing them to process small amounts of additional fluid safely.
When beginning, water should be offered only in small quantities, such as a few sips with meals, and should not exceed four to eight ounces per day. The purpose of introducing water at this stage is primarily to encourage the use of a cup and to help the baby learn the taste of plain water. Milk or formula must remain the main source of hydration and nutrition until the baby is at least 12 months old. Introducing water also aids the digestion of solid foods and can help prevent constipation as the diet diversifies.