An analysis of the existing Osijek water supply system was carried out. That analysis covers all relevant physical and partially chemical processes in the process of water treatment. After having carried out the analysis, more attention was given to requests regarding regulation of certain physical and chemical variables in the water treatment process. A complete mathematical model of the water supply plant for ground water intake as well as water treatment has been created. Verification of the mathematical models was performed by comparing the response of the model with the response of the water supply plant. Operation principles of the predictive control regulator was described and then the algorithm of the General Predictive Control regulator (GPC) adjusted to the realization on the PC was worked out. A procedure of implementation of the general predictive control regulator was described within the Osijek water supply system. The way of solving the problem of controlling the water plant intake, transport and water treatment was applying the GPC regulator to the system was also shown. Simulation results of the water supply plant model, confirmed a possibility of a higher level of supervision of the process control and reduced production cost. The response of the water supply plant model controlled by the GCP was compared to the response of the water supply plant controlled manually by the operator. An analysis of the existing water supply plant for ground water intake and water treatment was carried out with an emphasis on the possibility of improving the existing processes, in order to increase supervision over sub processes and the quality of the overall process. Guidelines for further development of the water supply system of the City of Osijek were given, with respect to the improvement of the quality of drinkable water and the cost-effective process in water treatment.