This article shows the hydraulic and mechanical study of the turbine of a typical Spanish watermill. The mill in question is located in Alcala Real (Jaen, Spain), and shows the common characteristics of Spanish watermills. Given its state of abandonment, we developed a virtual model of the mill, in 3D and with computer animation which helps to show how the mill worked. We also give a comparison with Spanish windmills, showing way the two types of technology coexisted as a way of milling grain, and we give data on the performance of both technologies (c) 2007 Elsevier Ltd. All rights reserved.