Household water treatment (HWT) has the potential to reduce waterborne diseases in developing countries. In this article, factors from social–psychological theories are analyzed in order to design effective interventions that promote HWT. Two treatment behaviors—solar disinfection (SODIS) and boiling—are compared with untreated-water consumption using data from a SODIS campaign in Bolivia. The main drivers of intention are affective beliefs, health beliefs related to untreated water, and descriptive norms. Behavior is primarily influenced by the habit related to each water type. Strong interrelations between beliefs and the habit related to one water type and the intention or consumption related to the others exist. Future campaigns should not only promote the target health behavior, but also investigate predictors of the health-risk behavior in order to prevent it.