Abstract: The primary aim of this study was to investigate the effect of ultrasonic reactor (USR) at different sonication times on HPC. Heterotrophs are broadly defined as microorganisms that require organic carbon for growth. A variety of simple culture-based tests, which are intended to recover a wide range of microorganisms from water, are collectively referred to as heterotrophic plate count or HPC. USR is able to inactivate bacteria through a number of physical, mechanical and chemical effects arising from acoustic cavitation. Results showed that a significant increase in percent kill for HPC bacteria with increasing duration of sonication in 42 kHz after 90 min sonication.