When properly prepared, all infant formulas are approximately 85% water. Infant formulas are available in three forms: liquid ready-to-use, liquid concentrate, and powder concentrate. Liquid ready-to-use formulas do not require the addition of water, while the liquid and powder concentrates require the addition of water. It is of prime importance for parents to read, understand, and follow the manufacturer's directions when adding water to liquid and powder concentrates.
Too much water: Adding too much water to these formula concentrates or adding water to ready-to-use formulas can lead to water intoxication in the baby. In severe cases, water intoxication can cause low blood sodium levels, irritability, coma, and even permanent brain damage.
Not enough water: failing to adequately dilute the concentrates with water causes the formulas to be too "hypertonic." Hypertonic formulas can induce diarrhea and dehydration. In extreme cases, ingestion of overly hypertonic formulas can lead to kidney failure, gangrene of the legs, and coma.
Therefore, parents should not adjust the amount of water that is added to concentrates to either "fatten the baby up" or "put the baby on a diet." Instead, parents should discuss their concerns regarding the baby's calorie intake with his/her pediatrician.