In this paper, the potential for Cryptosporidium passage through filters during periods of suboptimal coagulation is reported. The removal of Cryptosporidium was measured relative to the removal of particles, turbidity, and bacillus subtilis spores. Evaluating the sensitivity of the coagulation process allows for a description of the robustness of pathogen removal. Robustness is defined as the ability of a filtration system to provide excellent particle and oocyst removal during stable operating conditions and to deviate minimally from this performance during process upsets. Quantifying treatment robustness can serve as a practical tool for optimizing treatment strategies. Includes 10 references, tables, figures.