The objective of this paper is the assessment of CT values required for the inactivation of C. parvum oocysts with free chlorine and monochloramine in single-step and sequential disinfection schemes. The primary disinfectant used for sequential disinfection is ozone. Oocyst viability was determined by a modified in-vitro excystation method demonstrated to be consistent with animal infectivity data. Experiments were performed to investigate single-step disinfection with ozone, free chlorine and monochloramine, and sequential inactivation with ozone/free chlorine and ozone/monochloramine. Inactivation and ozone pretreatment experiments were conducted with a semi-batch reactor and analytical components.