Heterotrophic plate counts (HPC) in drinking water distribution systems: A comprehensive review and meta-analysis

Abstract

ABSTRACT Heterotrophic plate count (HPC) is widely assessed in drinking water distribution systems. However, methodological standards and guidelines on the use of HPC are not clearly defined. This comprehensive review and meta-analysis aim to evaluate HPC concentration and how they relate to the characteristics and operational conditions of systems. The size of the distribution system, use of chlorine or chloramine as secondary disinfection and the carbon content of the water were considered. Among 839 MEDLINE® records, 39 met our criteria and were included in the meta-analysis. Overall, wide ranges of HPC levels were observed in drinking water distribution systems. Results from the meta-analysis show a significant difference in concentrations between systems using chlorine or chloramine as secondary disinfectant and those that are not using any form of secondary disinfection. Similarly, results demonstrate a positive correlation between HPC levels and assimilable organic carbon. Assessing the spatial and temporal variations of HPC can provide useful information about the biological stability of the water and allow for routine analyses within individual drinking water systems. Due to its limitations as a global and unique indicator of water quality, HPC should be applied as part of a multi-parameter approach for microbial growth analysis in distribution networks.