Devise your cast of characters. You need a sun, as well as water drops in a variety of situations, for example in the ocean, as snowflakes, as ice in a glacier and in a river. Clouds and vapor are also essential. If you need extra roles to have enough for all your students, add heat, cold and gravity to the list.
Write a short vignette for each group of water drops, dividing the lines between as many drops as possible. Begin with drops in the ocean discussing how nice and cool they are. Have the sun talk about how warm he or she is. Have the sun invite the water droplets up to play, and have the droplets begin speaking in unison as they become a cloud.
Instruct the cloud break apart into snowflakes, who talk about how individual they each are. Have gravity enter and announce that he is pulling the snowflakes down; they announce that they are falling slowly. Have them speak in unison as an ice floe and talk about how long they are likely to remain frozen.
Add a new scene for each part of the water cycle process, making sure that all children are included. After the ice formation, have heat enter and say that the sun has sent her. The Sun can apologize for taking so long to get there as the ice floe splits into individual river drops, who talk about rushing off in different directions and seeing different parts of the world.
Have the ocean drops enter again and greet each other, and recap all the places they have been since they were last in the ocean. When the sun and heat enter again, have the ocean drops announce that they are evaporating once more.
Add stage directions to your script. Direct heat to rub the arms and shoulders of the ocean drops as though to warm him up, and ask direct vapor drops and snowflakes to clump together when they become the cloud and the ice floe. Direct cold to blow on the cloud to cool it off, and ask gravity to gently pull snowflakes downward as river drops to disperse around the room. The main thing is to keep your actors active.
Cast your students in the various roles. Choose your gentlest and most well-behaved students for Gravity, Heat and Cold.
Write a set of comprehension questions to give to students after they enact the play. Include questions like "What is the name for the step in the water cycle where ocean drops become vapor?" and "Where is it more likely to rain and where is it more likely to snow?"