Gather the following materials: a large bowl, a small (baby food) jar, rubber band, plastic wrap and a few ounces of water. Fill the bottom of the large bowl with water. Place the small jar on the bottom of the large bowl, making sure that the water in the bottom of the bowl does not flow into the jar. Cover the jar with the plastic wrap and secure it in place with the rubber band. Place the small weight in the middle of the plastic covering. Set the bowl in a sunny place. Observe the bowl each day and note what happens inside of the small jar. (You will see that the sun warms the water causing it to evaporate, the water condenses on the plastic wrap, then falls back down in droplets into the small jar.)
Place a pot of water over medium heat on a stove. (This step should be performed by an adult.) As the water heats, you see steam rise from the pot. That steam is evaporated water.
Over the same pot of boiling water described in Section 2, hold something made of glass, such as a small mirror, in place. (This step should be performed by an adult.) Water droplets will gather on the glass object. The water on the mirror is condensation.
As you continue to gather droplets of water on the glass object described in Section 3, the water will fall back down. The water falling back down from the glass object is precipitation, which occurs in nature as rain. Explain this concept to your fourth grader.