Extend the Activity Synthesis of Activity 1, “Estimate the Volume of Containers,” by asking students to think about ways to reduce the amount of water that people use. (Fix leaky faucets. Turn off water while brushing teeth. Take shorter showers. Collect rain to water the garden. Plant native plants.) If not mentioned by students, point out that putting a brick in the back of the toilet tank is another way to save water. Ask students how they think this works. (The brick takes up volume in the tank in place of the water.)