Dramatically show your students the incompressibility of a liquid. Shake the Water Hammer up and down and an unexpected sound will be produced—the “ping” of a hammer hitting a nail. Students will suspect that this is a trick, but will be amazed to learn that it is only water causing the noise—no other objects are used. Students may have even heard the phenomenon known as water hammer in the water pipes of their home, and now they will be able to explain it. The Water Hammer is a great device to introduce students to concepts, such as water pressure, fluid properties and resonance. Demonstration instructions and background information are provided.