The SWTR(Surface Water Treatment Rule) requires surface water treatment plants to achieve a 3log removal of Giardia cysts and 4log removal of viruses based on filtration, maintenance of CT[disinfectant concentration(㎎/L)×time(min)] through the disinfection process. Conventional treatment without disinfection is capable of achieving up to 2∼3log removal of Giardia cysts and up to a 1∼3log removal of viruses. Additional removals must be accomplished with disinfection(C×T value). Tracer-test was used in this study to calculate T_(10) of C×T value for achieving up to a 1log removal of Giardia cysts in disinfection process. Evaluations were implemented at three WTPs(Water Treatment Plants A, B, C). If CT product for a WTP meets or exceeds those in the SWTR tables, it is assumed that the degree of inactivation has been achieved. A WTP has not been achieved for the degree of inactivation result from CT_(cal)/CT_(req)=0.7 and the three WTPs have not been achieved for the degree of inactivation in worst case condition.