The heterotrophic plate count (HPC) test is a method used to measure the number of heterotrophic bacteria present in drinking water. This test involves growing bacteria from a water sample on a nutrient-rich agar plate, and then counting the number of colonies that form. The standard test method for HPC is the Standard Methods for the Examination of Water and Wastewater, which is published by the American Public Health Association (APHA). The HPC test results are usually reported in colony formi