Put a jar outside when there is a heavy period of rain. Leave the jar outside for an hour and ask the children how much rain, in terms of inches, they think is in the jar. Let them study the rain in the jar by looking at it, and ask them if they think it looks any different than the water they use at home. When the children have given their answers, explain to them why rain is important to human beings.
Ask the children where they think rain comes from and how they think rain is made. Question the children about what they think a cloud is made up of, and what is likely to happen if a cloud is black. Ask the children if there is likely to be any rain when there is a cloudless, blue sky. Describe the process to the children of how rain forms in clouds, and why the blacker a cloud is the more likely it is to release rain.
Show a DVD to the children that features different types of rain falling, from a brief shower, to a steady drizzle and then to a torrential rain. Ask the children whether drizzle or torrential rain will make the biggest puddles, and why. Let the children speak about their own experiences of being outside when it rains. Ask them what types of rain they have experienced and whether they enjoyed the experience or not.
Bring to the class a potted plant and ask the children what would happen to the plant if it went without water. Describe how water is a very important element in sustaining life. Ask the children what would happen to an area if it went without rain for a long time. Show the children a photograph of a desert and explain that deserts are a consequence of an area not receiving much, if any, rain.