According to the Institute of Medicine's Dietary Reference Intakes for Electrolytes and Water, the Adequate Intake (AI) for water for children aged 1 to 3 is 1.3 liters per day; that's about 44 fluid ounces, or the equivalent of 5-1/2 8 ounce cups of water.
Baby’s can be introduced to water at 6 months of age.