After defining the water mill and the reasons for its construction, I describe its design and operation; its social, heritage and economic impacts were then tackled. The research was based on field investigations and site visits to more than 20 water mills in Lebanon. Data of their features, their geographic location, owners and current situations were collected; models and maps were then implemented. The oral investigation was one of the ways to understand the logic behind the mills’ techniques and its different impacts. Finally, I explain popular expressions and terms related to water mills.