Abstract The aim of this study was to evaluate the effectiveness of the coagulation process in reducing the level of pollution of surface water with organic substances. The coagulants used in the study were aluminium sulphate and pre-hydrolyzed polyaluminium chlorides PAX. Powdered activated carbons with trade names AKPA and CWZ were used for the enhancement of coagulation. Lowering the total organic carbon (TOC) content in water after the coagulation was in the range of 15–45%, and the oxygen consumption in the range of 27–63%, depending on the used coagulant. The largest reduction in values of those indicators were stated using PAX. In the surface water subjected to chlorination, presence of CHCl3 and CHCl2Br was demonstrated, and CHBr3 and CHClBr2 were not detected. CHCl3 and CHCl2Br concentration was equal to 65.3 and 7.4 μg/L, respectively. In the water subjected to chlorination after the coagulation process and after the process of coagulation enhanced with powdered activated carbon, CHCl3 concentration ranged from 55.8 to 39.8 μg/L, while CHCl2Br ranged from 7.8 to 9.0 μg/L. These were values by 13–35% lower than trihalomethane (THM) concentration obtained in untreated surface water subjected to chlorination. The lowest CHCl3 concentration were obtained in chlorinated water after prior purification with PAX-XL19 and powdered activated carbon CWZ.