Abstract: An optimized mathematical model is essential to the planning of waste-water treatmentsystem. In this paper such a model bas been proposed on the basis of heuristics combined with gradient methodology. It is applicable to systems characterized by linear constraint conditions and non-linear objective conditions—homogeneous treatment, optimized treatment and regional treatment. Thecorresponding computer programs may provide relevant matrix of water quality restriction equations,costs of waste water transport and treatment, and body water quality parameters. Applicatian of the model and analysis of its sensitivity have been given together with a practical example.