This slide presentation outlines a study on microbial behavior in distribution system biofilms and focuses on these topics: current state-of-knowledge for phases of the biofilm cycle; explore "who is there and what they do"; explore adaptation of microorganisms in biofilms; draw on increasing numbers of distribution system (DS) biofilm studies; and, the potential risks for treatment and for consumers. Specific topics include: overview of biofilms in distribution systems; advantages of biofilm habit; microbe changes on attachment; early colonization; effects of pipe material; disinfectant residual; changing disinfection regimes; community expansion; mature biofilm; competition and cooperation; communication and blocking; predation; pathogens persisting in protozoa; dispersal; who is there and what they do; coliforms and E. coli; corrosion; nitrification and denitrification; and, potential risks.