The present work had the objective of modelling and optimizing model-based industrial water circuits (IWC). The IWC consist in streams of production processes that commonly are treated as secondary circuits, and, consequently, the related energy consumption is being neglected and, so of, a great optimization potential. In the scope of the European funded WaterWatt project, eleven cases were investigated, and the water circuits models were assembled in OpenModelica, by creating a custom library from components of the ThermoPower library. The current work focuses on the five more representative cases studies of the project. These models were properly calibrated through real measured data and improvement measures were applied to increase energy efficiency. The energy efficiency improvement-driven optimization was executed by adapting the pump motors speed, in case of variable water demand circuits, and the cooling tower fans speed, in addition to increase mechanical and hydraulic efficiencies of the pumps. This allowed a total share of energy savings of 25%, 4%, 23%, 17% and 12% for, respectively, the open cooling circuits, closed cooling circuit, gas washing circuit, transportation circuit and quenching circuit, for the case of the application of variable speed drives in pump motors and cooling tower fans simultaneously with the change to high efficiency motors. An identical implementation procedure was executed for the application of variable speed drives simultaneously with the refurbishment of pumps, in which was possible to achieve a total share of energy savings of 31%, 13%, 32%, 24% and 12% respectively for each one of aforementioned circuits.