In order to manage microbial risk in a water supply, it is important to determine the physical removal performance of the water treatment process. In this study, results from three separate research projects were assembled to determine the overall fate of microbial pathogens entering a conventional water treatment plant. In order to quantify the physical log-removals of each unit process, a number of spiking trials were carried out at both pilot and full-scale over a two-year period. Particles used in spiking trials included Cryptosporidium parvum oocysts (formalin inactivated), Total Coliform and E.Coli bacteria (native in raw water), B.subtilus, and polystyrene microspheres. Under normal treatment conditions, microbial removals were found to be 6.4-log for Cryptosporidium and other similar particles, whereas removal performance decreased to 3.5-log during impaired coagulation conditions. Waste sludge experiments were also conducted to determine the fractionation of C.parvum oocysts between the solids and supernatant phases of sedimentation sludge and filter backwash waste. During the course of the study, several new techniques were developed that can be used to determine treatment plant performance for physical removal of microbial pathogens. Includes 5 references, tables.