From Aesop's Fables :The Crow & the Pitcher

A thristy crow found a pitcher with some water in it, but the water was so little that she could not reach it, it seemed like she was going to die of thirst, At last she thought of something, she picked up some pebbles and drop them into the pitcher, each time she dropped a pebble the water rose higher until the top, at last the crow was able to drink the water from the pitcher.