In a field experiment on water conservation, we aroused dissonance in patrons of the campus recreation facility by making them feel hypocritical about their showering habits. Using a 2 × 2 factorial design, we manipulated subjects "'mindfulness" that they had sometimes wasted water while showering, and then varied whether they made a "public commitment" urging other people to take shorter showers. The "hypocrisy" condition-in which subjects made the public commitment after being reminded of their past behavior-was expected to be dissonance-arousing, thereby motivating subjects to increase their efforts to conserve water. The results were consistent with this reasoning. Compared to controls, subjects in the hypocrisy condition took significantly shorter showers. Subjects who were merely reminded that they had wasted water, or who only made the public commitment, did not take shorter showers than control subjects. The findings have implications for using cognitive dissonance as means of changing behavior in applied settings, especially those in which people already support the desired goal, but their behavior is not consistent with those beliefs.