Granular activated carbon (GAC) in filter-adsorbers provides an excellent support surface for the proliferation of microorganisms. Bacteria proliferate on GAC even when prechlorination is practiced because GAC catalyzes the reduction of chlorine thus preventing bacterial deactivation. Moreover, laboratory studies have found that bacteria (including E. coli) attached to GAC taken from filter-adsorbers are resistant to disinfection. The concern is that some fragments of GAC (fines) can be released from filter-adsorbers and will have attached bacteria that are not inactivated by post disinfection. The objectives of this research are to examine the release of particles and attached bacteria from GAC filter-adsorbers and to determine if bacteria attached to the released particles can be disinfected. Particles were shown to escape from the GAC filter- adsorbers, but at very low concentrations. The data suggest that bacteria attached or associated with particles in product water from filter-adsorbers will not penetrate the chlorine barrier if particle concentrations are low.