The most commonly used membranes are of the "thin film composite" (TFC) type, consisting of three layers of polymers. Membrane modification has been explored through two main approaches: optimizing the polymer before fabrication or modifying the surface after fabrication. This study focuses on membrane modification by depositing ultrathin films of zinc oxide (ZnO) using the sputtering process. The impact on permeability and monovalent ion rejection is examined. The results show that an increase in ZnO deposition time leads to a reduction in permeate flux density, albeit with an improvement in monovalent ion rejection. The Spielger-Kedem model is demonstrated to effectively predict the behavior of these membranes. Collectively, the findings suggest that membrane modification with ZnO through sputtering can offer significant advantages in water purification applications, albeit with considerations regarding reduced permeate flux density.