A commercial thin‐film membrane (unmodified) of polyamide improved by poly(vinyl alcohol) (PVA)‐coated membranes (modified) was investigated for separating phenol in sour water by reverse osmosis. Dependences of pressure and pore surface area on flux and phenol rejection were tested. A graphical correlation was found between the relative flux decline and phenol concentration decrease in the feed. The modified membrane provided rejection of 86 % at 2 bar with the highest permeate flux of 8.46 L m−2h−1. The average contact angle for the former membrane was 58.4°, while that for the modified membrane was 49.1°. The reduction in contact angle enhances the surface hydrophilicity of the membrane leading to the antifouling effect. The modified membrane provides 95.4 % flux recovery compared to the unmodified membrane that provides only 66.2 %.