The effect of single trihalomethane (THM) (CHCl3) content in various types of water on the performance of two types of reverse osmosis composite membranes (the AFC99 membrane in tubular module Bl, PCI, and the FT30 membrane in a spiral-wound element BW3040, FilmTec) have been investigated. The performance of these membranes in RO tests carried out using distilled water, tap water and brackish water (1000-5000 ppm. NaCl) with the addition of THM have been evaluated in terms of permeate flux and the rejection of dissolved solids and THM. The FT30 membrane provided THM rejection better than 99.5% during the reverse osmosis treatment of tap water and brackish water. The AFC99 membrane exhibited only 80% retention of THM, obtained for the transmembrane pressures in the range of 10 to 30 bars. It was found that the presence of CHCl3 slightly affects the transport and separation properties of the composite membranes used.