The present application provides a method of optimizing fan usage in a cooling water system having a number of fans with a heat exchanger to cool a cooling fluid for use with a number of gas turbine subsystems. The method may include the steps of running all of the fans at base load, calculating a heat transfer capability of each fan at base load, calculating a temperature difference between an actual temperature and a target temperature of the cooling fluid, selecting a minimum target temperature of the cooling fluid, calculating a target thermal energy of the cooling fluid for the minimum target temperature, calculating a number of the fans to be turned on or off by dividing the target thermal energy with the heat transfer capability of each fan, and turn on or off the calculated number of fans in a predetermined manner with an objective of balancing the running hours of each fan.