The content of assimilable organic carbon (AOC) has been proposed to control the growth of heterotrophic microbe in drinking water distribution systme. However, recent results have shown that there are regions where it is predominantly phosphorus which determines the extent of microbial growth in drinking water. The growth of bacteria was studied in a drinking water distribution system where the content of AOC was high (40.84- 551.35 μg acetate-C/L) and the content of Microbially Available Phosphorus (MAP) was also high (0.69-8.01 μg PO43--P/L). It was AOC other than phosphorus that controlled the growth of bacteria in the drinking water distribution system. Comparably obvious linear relationship was found between the maximum HPC and the maximum content of AOC of the distribution system. Removal of organic matters is ideal approach to control water quality of the drinking water distribution system.