Bacteriology of drinking water distribution systems: an integral and multidimensional review

A drinking water distribution system (DWDS) is the final and essential step to supply safe and high-quality drinking water to customers. Biological processes, such as biofilm formation and detachment, microbial growth in bulk water, and the formation of loose deposits, may occur. These processes will lead to deterioration of the water quality during distribution. In extreme conditions, pathogens and opportunistic pathogens may proliferate and pose a health risk to consumers. It is, therefore, necessary to understand the bacteriology of DWDSs to develop effective strategies that can ensure the water quality at consumers' taps. The bacteriology of DWDSs, both the quantitative growth and the qualitative bacterial community, has attracted considerable research attention. However, the researchers have focused mainly on the pipe wall biofilm. In this review, DWDS bacteriology has been reviewed multidimensionally, including both the bacterial quantification and identification. For the first time, the available literature was reviewed with an emphasis on the subdivision of DWDS into four phases: bulk water, suspended solids, loose deposits, and pipe wall biofilm. Special concentration has been given to potential contribution of particulate matter: suspended particles and loose deposits. Two highlighted questions were reviewed and discussed: (1) where does most of the growth occur? And (2) what is the contribution of particle-associated bacteria to DWDS bacteriology and ecology? At the end of this review, recommendations were given based on the conclusion of this review to better understand the integral DWDS bacteriology.