This research study focused on enhancing slow sand filter (SSF) performance and, in particular, organic precursor removals using gravel roughing filters (GRF) with the addition of ozone or a coagulant. A series of pilot SSF and GRF columns were assembled at a highly colored water source in selected configurations to compare performance. Overall removal of organic precursor material and filter run times for the selected pretreatment options were evaluated and compared. In addition, for comparison purposes, the performance of a slow sand filter with an embedded layer of granular activated carbon (SSF with GAC) was also evaluated. Includes 3 references, tables, figures.