A mathematical model was developed to quantify Cryptosporidium, Giardia and E. coli loads in the Wingecarribee watershed, which is part of the drinking water watershed serving approximately 4 million residents in Sydney, Australia. The model describes the relative significance of different sources of the pathogens as well as their fate and transport as they move through the sub-watersheds. The estimation of pathogen transport rates from fecal deposits to waterways via surface runoff was identified as an important component of the model. Experiments were conducted using artificial rainfall simulation to determine the rate of Cryptosporidium, E. coli and PRD1 bacteriophage transport from bovine fecal pats. Future work will focus on testing the model to calibrate those components with the highest level of uncertainty, including rates of direct fecal deposition, connectivity of on-site systems and rates of manure mobilization for other types of animals. The pathogen model will enable water utility managers to identify those watershed segments that contribute the highest load of pathogens and where management options will be most effective. Includes 15 references, table, figures.