The objective of this research program was to obtain realistic information concerning the interrelationships between temperature, chlorine, turbidity, coliforms, and Standard Plate Count (SPC) densities present in finished water after treatment and distribution. Bacterial identifications were performed to determine types and densities of isolates from the SPC and coliform tests. The frequency of coliform isolation was independent of free chlorine, turbidity, and temperature. SPC were not contingent upon low level turbidity and varied with respect to free chlorine residual and temperature. SPC exhibited no interrelationship with coliform counts (MF) when the SPC was less than 50 organisms/mL. A slight inverse relationship was noted between free chlorine residual and turbidity. Of the physical and chemical parameters measured, free chlorine residual had the greatest influence on the microbial population. Encapsulated Klebsiella pneumoniae, Enterobacter agglomerans, Enterobacter aerogenes and Enterobacter cloacae exhibited the ability to survive a free chlorine residual of 0.2 mg/L or more. The diversity of organisms identified by the SPC method strongly suggests the phenomenon of an established microbial ecosystem with the distribution networks.