The water cycle. Drip the water drop and his adventure through water. This would good for older students. or grade. This could also be tied into a social studies lesson in order to help understand what is going on as Drip travels along the water.
One of our favorite water cycle illustrations, especially for younger students. The image of the sun's rays reaching down to draw up water is a great way to represent evaporation. It highlights the driving force of the sun.