In this paper, a decision-support tool named HYDROPTIM has been developed that allows the flowmanagement in a large scale water systems including reservoirs, open channels for water transport,water treatment plants, pressurized water pipe networks, tanks, flow/pressure control elements and atelemetry/telecontrol system. Predictive optimal control is used to generate flow control strategies fromthe sources to the consumer areas to meet future demands with appropriate pressure levels, optimizingoperational goals such as network safety volumes and flow control stability. The tool allows as well tobuild the network model graphically and then to automatically generate the model equations used bythe predictive optimal controller. Additionally, the tool can work off-line (in simulation) and on-line(in real-time mode). The case study of Guadiana River is presented to exemplify the control resultsobtained using the tool.