Membrane technologies for water treatment are becoming increasingly attractive for obtaining high-quality drinking water. Considering the increasing demand for water due to population growth, industrialization and climate change, in the last decade, reverse osmosis (RO) has been the predominant desalination method for obtaining drinkable water from the sea and brackish waters. However, RO technology faces disadvantages such as relatively low water fluxes that commercially available membranes have. The use of existing highly permeable membranes is not an option for obtaining larger amounts of water because they have insufficient selectivity of salts and other components. Therefore, membrane technology is currently searching for new membrane products, new materials and ways of preparing highly productive, and at the same time, highly selective membranes. There are several ways to overcome the trade-off between selectivity and permeability, one of which is solvent activation of the membrane material. This method is efficient, economical and is increasingly being investigated and used to improve membrane performance. In this work, the influence of organic solvents, specifically alcohols, on commercial thin-film composite polyamide (TFC-PA) RO membranes and their performance is studied. Changes in the water flux through the membrane and the retention factor of NaCl and CaCl2 before and after the activation of the membranes with selected solvents were determined experimentally using a laboratory scale RO system. With short-term contact of the activation solvent and the membrane for 5 and 60 minutes, it was achieved an increase in water flux with no significant effect on the retention factor of inorganic salts. The influence of activation on the retention factor of N-nitrosamines, potentially carcinogenic compounds that are not welcome in water and therefore need to be removed, was determined experimentally, for which RO seems to be the most suitable method. A minimum of 90% retention of selected N-nitrosamines was determinded.