For the treatment of surface water, the coagulation process was used with highly alkaline polyaluminium chloride PAX-XL19F and coagulation supported by ozonation and adsorption on powdered activated carbon CWZ-30 for reducing the level of surface water pollution with organic substances. In addition to the typical indices used to assess the content of organic compounds (total organic carbon TOC, oxidisability OXI, ultraviolet absorbance UV254), the study also evaluated colour, turbidity, and the potential of trihalomethanes formation THM-PF. Reduction in the content of TOC in water after coagulation ranged from 22 to 24%, OXI - in the range of 34-36%, and UV254 absorbance - from 52-55%. The turbidity and colour of the water was reduced by 70-73% and 56-60%, respectively. The use of preliminary ozonation and activated carbon-assisted coagulation increased the efficiency of water treatment. Changes in the values of TOC, OXI, UV254 absorbance, turbidity and colour were 28-33%, 45-46%, 69-73%, 72-79% and 89-100%, respectively. In the water purified by coagulation and then chlorinated, THM-PF was 37-38% lower than in untreated surface water. The use of additional pre-ozonation and activated carbon during coagulation increased the reduction of THM-PF by 9-12%.