Variations of bacterial communities and pathogen levels in drinking water treatment processes with the impact of seasons and extreme weather events

Drinking water treatment processes have been reported to effectively improve water quality, but there is still a pathogen risk in treated water, especially after extreme climate events. The goal of the study was to identify the shift of bacteria and pathogens in source and treated water over a year including when extreme weather events occurred. Water samples were collected from Yangtze River Delta area and a local full-scale drinking water treatment plant. The microbial community structure and the occurrence of pathogens were investigated in samples using 16S rRNA sequencing and qPCR techniques. The results showed the intense rainfall can significantly increase levels of bacteria and pathogens in river and treated water samples from major processes and percentage of Cyanobacteria raised remarkedly during the super typhoon event. Opportunistic pathogens Legionella spp. and Mycobacterium spp. were detected in all river samples and some finished water samples, while their concentration increased after rainfall. Our results suggest that finished water quality needs more organized attention and engineering strategies needs more precise concern for protection of human health under the changing climate.