The design, operation, and performance of granular activated carbon (GAC) filter-adsorbers were documented and potential problems were identified by means of a survey of operating plants and a review of the literature. It was found that GAC as a total or partial replacement for sand is as effective as conventional filtration media for removing turbidity, provided an appropriate medium size has been selected. In addition, filter-adsorbers can consistently eliminate tastes and odors from water supplies for extended periods of time. Sand-replacement filter-adsorbers, however, do not function well for removing less strongly adsorbed compounds such as trihalomethanes, volatile organics, and fractions of total organic carbon. More research is needed to determine whether microbial growth in filter-adsorbers is beneficial or detrimental. Includes 39 references, tables, figures.