Water companies make efforts to reduce the risk of microbial contamination in drinking water. A widely used strategy is to introduce chlorine into the drinking water distribution system (DWDS). A subtle potential risk is that non-lethal chlorine residuals may select for chlorine resistant species in the biofilms that reside in DWDS. https://www.roneverhart.com/HGST-Ultrastar-7K6000-HUS726040ALS214-4TB-7-2K-RPM-SAS-12Gb-s-512n-128MB-3-5-SE-Hard-Drive/