Infants under six months of age should not be given plain water. This standard medical recommendation is based on two primary concerns related to the unique physiology and rapid growth demands of a newborn. Breast milk or infant formula provides all the necessary hydration and nutrition a baby requires during the first six months of life. The fluid in milk is perfectly balanced to support development without taxing the infant’s immature body systems.
Nutritional Priority and Displacement
The first major reason for withholding water relates to the infant’s high caloric and nutrient density requirements. Infants experience unparalleled growth, demanding about 100 calories per kilogram of body weight daily. This immense energy need must be met with nutrient-dense sources, which breast milk and formula provide.
An infant’s stomach is small and holds a limited volume of liquid at each feeding. Introducing water, which contains zero calories, displaces the volume of nutrient-rich milk the baby could have consumed. Since milk provides the necessary fats and carbohydrates for development, reducing milk intake results in a substantial loss of fuel for brain and body growth.
Consistently giving water can lead to insufficient calorie intake, potentially resulting in slow weight gain or a failure to thrive. Milk itself is primarily water, with mature breast milk being about 87% to 88% water. This high water content naturally satisfies the infant’s hydration needs without the need for additional plain water.
The Physiological Risk of Water Intoxication
Giving water to a young infant poses a serious physiological risk due to the immaturity of their renal system. A baby’s kidneys are not fully developed and are inefficient at filtering large volumes of water. Their ability to regulate the balance of water and electrolytes, particularly sodium, is limited.
When an infant consumes too much plain water, it rapidly enters the bloodstream and dilutes the concentration of sodium. This condition is known as hyponatremia, or water intoxication. Sodium is an electrolyte necessary for proper cell function, including nerve and muscle signaling.
The dilution of sodium causes water to rush into the cells to balance the concentration gradient. When this happens in the brain, the cells swell. This is dangerous because the skull cannot expand to accommodate the increased volume. Symptoms of hyponatremia include irritability, drowsiness, apathy, and vomiting, and in severe cases, it can lead to seizures, coma, and death.
Guidelines for Water Introduction
The appropriate time to begin offering water is around six months of age, coinciding with the introduction of solid foods. At this stage, the infant’s kidneys have matured sufficiently to handle small volumes of additional fluid. Water is primarily offered to help the baby learn to sip from a cup and to accompany the new solids being added to their diet.
The quantity of water should be limited to small sips offered with meals. Pediatric sources suggest an initial limit of no more than four to eight ounces of water total per day for babies between six and twelve months. Formula or breast milk must remain the primary source of nutrition and hydration throughout the first year, even after solids are introduced.