The Heterotrophic Plate Count (HPC) is used to count total bacteria in water under certain growth conditions (media and temperature). This method is specifically applicable for the analysis of drinking water sources under EPA’s Surface Water Treatment Rule (40 CFR 141.7) and reagent water used in microbiology laboratories, but may also be used for other water and wastewater. 

HPC can be used to monitor changes in the bacteriological quality of finished water throughout a distribution system, thus giving an indication of the effectiveness of chlorination or other disinfection in the system, as well as the possible existence of cross-connections, sediment accumulations and other problems within the distribution lines. 

HPC is also used to evaluate the effectiveness of biocides in cooling water systems. Types of water that may be tested include; potable water, swimming pools, spas, cooling towers, and reclaimed water.

Test Method 

  • Enzyme Substrate Method, incubation 35°C ± 0.5°C for 2–3 days in humidified air.  
  • Standard Methods for the Examination of Water and Wastewater: Method 9215E.
  • Measure of uncertainty available upon request.

Turn Around Time

2–7 days

Test Code


Sample Instructions and Shipping

HPC sample collection for water systems and cooling towers and compliance testing for drinking water require different procedures. For instructions see HPC Sampling and Shipping.