This book provides a critical assessment of the role of HPC measurement in drinking water quality management. The HPC test (or Standard Plate Count), applied in many variants, is widely used to measure the heterotrophic microorganism population in drinking-water and other media. Heterotrophs are organisms, including bacteria, yeasts and moulds, that require an external source of organic carbon for growth. This book provides valuable information on the utility and the limitations of HPC data in the management and operation of piped water systems as well as other means of providing drinking water to the public. It is of particular value to piped public water suppliers and bottled water suppliers, manufacturers and users of water treatment and transmission equipment and in-line treatment devices, water engineers, sanitary and clinical microbiologists, and national and local public health officials and regulators of drinking water quality.