A building plumbing rig experiment simultaneously examined how water temperature (cold/hot lines), influent disinfectant residual (0-1 mg/L chloramine), flow rate (0.5-2.2 gpm), and water retention time (WRT) of 0-17-days impacted water quality at the point of use. In cold water lines with no disinfectant, WRT was a key driver of bacterial growth, with total cell counts (TCC) in the water increasing by up to 20× relative to influent water at 6.7-days WRT. A chloramine residual in cold influent water suppressed the maximum TCC by about 50%, even after the residual was no longer measurable. When the water heater set point was warm (40 °C) with minimal or 1 mg/L Cl