Heterotrophic bacteria are common microorganisms in water. While usually harmless, high levels can indicate water quality issues or bacterial growth in pipes and storage tanks.

Heterotrophic bacteria are measured using the Heterotrophic Plate Count (HPC) method. These microorganisms occur naturally in the environment, including water sources. While generally not harmful, their presence in high numbers can signal water quality problems or bacterial growth within distribution systems. They can multiply in pipes, filters, and storage tanks, making HPC a useful indicator of overall water system cleanliness. Water treatment processes aim to control heterotrophic bacteria levels to ensure safe, high-quality drinking water.