Water-cooled packaged air conditioner systems are gaining renewed recognition from the perspective of preventing the urban heat island phenomenon. Up to now, however, there have been no reliable methods for optimizing equipment capacity. For this reason, in telecommunications buildings, which demand high levels of reliability, there are cases of excessively redundant configurations, which not only result in reduced space efficiency, but also invite reduced operating efficiency due to partial load operations. In a previous report, we constructed a model for evaluating water-cooled packaged air conditioner systems, and demonstrated that it was possible to study equipment configurations based on these reliability evaluations. In this report, using this reliability evaluation model, we showed the equipment configurations required for each level of reliability. Furthermore, we proposed a design process using the reliability evaluation methods in this research, taking into account reduced capacity of the cooling tower resulting from the passage of time.