A great experiment to illustrate soil erosion! This simple experiment shows the importance of trees as a part of our environment. The water that runs through soil with vegetation (left corner), comes out clear, while the other two without vegetation is muddy.
Pour a cup of hot (but not boiling) water into a clear glass jar and immediately cover with a plate. Wait a few moments, then place ice cubes on plate. Warm air can hold water in the gas phase better than cold air, so as the vapor cools, the water will condense down into the jar.