Istanbul Water and Sewerage Administration have been conducting studies on advanced treatment methods in order to increase the quality of the effluent water in the treatment plants and to provide drinkable water to citizens. In this study, five-year operating costs of nanofiltration (NF) and granular active carbon (GAC) adsorption processes were calculated. The investment cost of the GAC adsorption process requires approximately 1.8 million $ more than the NF membrane process. The operation and maintenance (O&M) cost of the NF membrane process needs 1.1 million $ more than the GAC adsorption process. The O&M cost of GAC adsorption and NF membrane process is almost 5 times expensive than the conventional treatment process. By comparing these costs, conclusions were made on two different advanced treatment methods in terms of their cost-effectiveness and economic performance.