Biofilms are commonly found growing at relatively high densitieson surfaces within water distribution systems. The presence of biofilms within a distribution system does not necessarily indicate that the quality of the treated water has been compromised during transmission. Such films may be in monolayers or held within extra polymeric materials secreted by the bacteria which make up the film. Relatively little is known regarding the effect of flow regimes on biofilm densities. Of particular interest are those sections of a water distribution system which maintain low flow conditions due to limited use. This study was designed to determine the effects of varying flow regimes on culturable biofilms and planktonic bacteria in system dead ends in the presence and absence of free chlorine residual. Includes 8 references, figures.