The NYSERDA project "Optimization of UV Disinfection" has developed a software tool for analyzing the costs and performance of UV disinfection systems. The software, named UVCAT, provides simulations of UV system performance as a function of time factoring in flow and UVT data, lamp aging and sleeve fouling, dose monitoring and control, and UV system component performance and costs. Outputs from the software include reactor and bank on/off status, power settings and consumption, lamp aging and fouling, and dose delivery over time. As the final task of the NYSERDA project, UVCAT was further developed as a UV system risk analysis tool. UVCAT was modified to include raw water pathogen concentration data and power quality data over time as inputs. Power quality data is entered as voltage and duration of power quality event. The UVCAT was also modified to include as inputs: voltage and duration of power quality events that cause UV system shutdown; use of UPS systems and generators including startup time; use of shutoff valves and valve closing time; lamp cool down and warm up times; daily probability of lamp, ballast, and UV sensor failure; and, population served by the water treatment plant. A new worksheet was added to UVCAT that includes a UV dose-response model for the pathogen, a human infection dose-response model, and an infection risk model. The UV dose-response model for the pathogen includes a field for the entered UV dose and a field containing a formula for the resulting pathogen inactivation. A general model that fits a wide range of UV dose-response data containing tailing and shoulders is provided in the paper. Includes table, figures.