I just did a quick google and got this,
http://www.earthsbest.com/toddler_nutrition/faqs/other.php
"How much water should my toddler drink every day?
According to the Institute of Medicine, a child between the ages of one and three needs about 1.3 liters of water a day. Keep in mind that total water intake reflects the sum of plain drinking water and the water content of all foods and beverages consumed during the day. That means your toddler may meet much of his water need from the milk, juice, fruits, soups, yogurt, etc. that he is eating. In order for your child to fulfill his fluid needs without an obligatory intake of unnecessary calories, be sure to offer plain water during meal and snack time, and between times in response to thirst. Many factors will affect your child's unique need for water including the climate you live in... a hot, dry climate will increase a child's need for fluid, activtiy level... active kids will need more water than sedentary ones, and fever or other physiological conditions may increase a child's need for water. Normal hydration can be maintained over a wide range of water intakes. The body has many mechanisms for achieving water balance. If not enough water is drunk, the kidneys will conserve water, and when fluid intake is high, urine output will increase. One way to make sure your child is drinking enough water is to pay attention to his urine output. If he is urinating frequently and the urine is pale yellow and with little smell, he's getting enough, but if his urine is bright yellow and acrid smelling, it's a good indication he's not getting enough fluid and his urine is very concentrated. Offer him plenty of plain, refreshing water to get back into balance. It's rare to get too much water and you needn't worry about that with a toddler who is allowed to drink in response to needs. "