Assessing the contribution of biofilm to bacterial growth during stagnation in shower hoses

Abstract

Stagnation occurs in building water supplies when there is little or no water usage. As a result, the number of bacteria increase, and this often leads to the deterioration of water quality. Still, the role of biofilm in stagnation remains unclear. This study used shower hoses as the model system and investigated the contribution of biofilm and microbes in fresh water to the bacterial growth in water under different stagnation times from 6 to 24 h. Bacterial counts in water were observed to increase significantly after 12 h stagnation but longer stagnation did not lead to further increase, indicating different mechanisms contributing to bacterial growth during stagnation. 16S rRNA gene sequencing and Sourcetracker2 further confirmed that the contribution of fresh water to the microbial core community did not increase significantly with stagnation time, whereas the contribution of biofilm increased significantly after 24 h stagnation (53.5%) compared with 6 h stagnation (11.2%) (p < 0.05). The present results differentiated the contribution between planktonic and biofilm phase to the bacterial growth during stagnation, and provided insights into its mechanism. These findings serve as a framework for future development of strategies to manage biological water quality at the distal end of the building water supplies.