Microbial Community Dynamics and Assembly: Drinking Water Treatment and Distribution

The supply of safe drinking water is a necessity for our societies. The microbiological quality of drinking water is the most important measure of water quality directly related to public health risks from waterborne diseases. Despite the long history of water research, the processes controlling microbiological quality of drinking water remain elusive to both researchers and practitioners in the field of drinking water treatment and management, representing a critical but long standing knowledge gap. The microbial communities in drinking water systems may be influenced by multiple processes including the source water, treatment barriers, persistence to disinfection, as well as biofilm development and detachment throughout the distribution system. Previous efforts, however, are mostly limited to only one of these processes, leading to inconsistent results and incomplete understanding as expected. Taking advantages of high-throughput metagenomics tools, this research for the first time applied a systematic approach linking all relevant processes to the microbiological quality of drinking water. It is revealed that the core populations of the sampled drinking water microbial communities are dominated by Alphaproteobacteria and Betaproteobacteria affiliated to the families of Methylobacteriaceae, Sphingomonadaceae, Comamonadaceae, and Oxalobacteraceae. The characteristics of the source water and the disinfection step in the drinking water treatment process train are found to be the most important factors controlling the bacterial community structure in drinking water. Despite its potential in enhancing the removal of microbial contaminants, membrane filtration as an increasingly popular treatment alternative to rapid sand filtration is not shown to have impact differing from that of conventional rapid sand filtration on drinking water microbial communities. The compositions of drinking water microbial communities examined in this study were dominated by a few very abundant species followed by a long tail of rare species, which is well represented by the Zipf-Mandelbrot model, accounting for 90% of the total variances and revealing low niche diversity in drinking water and distribution systems. Findings from this research provide much needed insight into the processes shaping the microbial communities in drinking water and the knowledge base for the development of effective strategies for the control of microbial contaminants in drinking water.