This paper describes the development of a spreadsheet model that simulates the recycle of filter backwash water in a water treatment plant and its impacts. The spreadsheet generates estimates of cyst concentrates at various locations in a treatment plant for five different recycle scenarios. The objectives were: to develop a screening model to identify important operation and design factors (including treatment and equalization of the recycle stream) that influence how backwash water recycle affects the accumulation of cysts; to determine how seriously backwash recycle may affect cyst accumulation (and breakthrough); and, to identify future research related to recycle of treatment residuals that could greatly increase the ability of the water treatment industry to understand and predict the effects of this practice on finished water quality. The model provides a "first-cut" method of comparing the effects of different recycle scenarios but does not capture all the operational complexities specific to a given plant that can affect the impact of backwash recycle. The remaining sections of this paper present descriptions, schematics, assumptions, and equations used in model development. Includes 5 references, tables, figures.