The relationship between the level of regrowth of heterotrophic bacteria and the level of easily assimilable organic carbon (AOC) was determined by collecting and examining a series of distribution water samples from 20 supplies during two summer and autumn periods. The AOC concentration of distribution system water decreased with increasing distance from the treatment plant, but AOC uptake was limited at concentrations < 10 ug C/L. A significant correlation was found between the concentration of AOC in water leaving the treatment plant and the geometric mean of the counts of heterotrophic bacteria in distribution water as determined on diluted broth agar medium. At AOC concentration < 10 ug C/L, the geometric mean of the colony counts on plate count agar medium (incubated at 22C) remained below the guideline value of 100 cfu/mL. Includes 43 references, tables, figures.