This publication issues a challenge to students to collect data in a nationwide analysis of water hardness. Background information on the chemistry of hard water is presented using a cartoon format, and each of the four activities contains an explanation about the chemistry illustrated in the activity. The effect of hard water on soap, the effect of calcium ions in water, the chemistry of a test strip, and the creation of a supersaturated solution are among the topics of the experiments. The publication also includes details about participation in the nationwide study and National Chemistry Week. (DDR)