The aim of presented research was to optimize the treatment process of the Prut River water. In order to realize the proposed goal, there were studied the following factors which can improve the process of coagulation: (i) the infl uence of stirring speed during coagulation and (ii) the infl uence of the concentration of the coagulant solution added in the process of coagulation. The optimal conditions of coagulation were established using the Jar-test method. Application of the recommended procedure contribute to the reduction of the coagulant dose, the contact time, the aluminum concentration in water and the expenses for water treatment.