The costs of granular activated carbon (GAC) filter-adsorbers (second-stage GAC filtration) were compared with those of the sand replacement option (first-stage GAC filtration). Simulation models of total organic carbon (TOC) adsorption and particle removal were used to describe filter performance. First-stage filtration was found to be the most cost-effective treatment option when TOC removals of less than 55 percent are sufficient. When treating waters with low TOC concentrations, using a large number of adsorbers in parallel, and regenerating the GAC off-site, first-stage filtration was found to be cost-effective for TOC removals as high as 75 percent. Second-stage GAC adsorbers should become more cost-efficient for removal of low concentrations of TOC as conventional filters for turbidity removal are designed at higher filtration rates.