We investigated an effect of the direct impact of a constant magnetic field on wastewater properties modification. Wastewater from two sources (differing in physical and chemical properties) was used in the experiment. Analyses regarded the impact of a constant magnetic field on the properties of wastewater prepared from powdered milk and on the composition of sewage taken directly from municipal sewage system. The experiment was carried out in the laboratory scale with the use of the technological systems comprised of magnetic activators of liquids. An obvious and regular reduction was observed in COD (25- 55%), chlorides (25–40%), N-NH4 (50-66%), P-PO4 to the values of 3.37-6.00 mg/dm3, and a considerable increase of Fe concentration. The parameters of both magnetically-treated wastewater types were modified to a similar degree and displayed analogous modification tendencies.