Reducing Water Age in Residential Premise Plumbing Systems

Water quality degrades with time as water travels to users through pipes. Water age (as a surrogate quality indicator) is not limited to distribution networks but carries through the residential premise plumbing system to the tap. Poorly designed premise plumbing layouts and intermittent usage patterns can lead to high residence times. This work aims to numerically quantify water age in residential premise plumbing systems using a stochastic demand simulator and a hydraulic solver. Plumbing layouts based on real houses are assessed and modified to determine design practices that lower water age. Results suggest that best practices are to loop the plumbing system or connect water closets at the end of the premise distribution branches to ensure periodic flushing. However, none of these approaches impacts the "last foot" of pipe connecting plumbing fixtures with the premise distribution pipes. The effect of fixture use intensity and water heater types on residence times is also assessed. The introduction of more efficient fixtures with their lower flows over the last several decades has increased residence times. On-demand heaters reduce water ages across all layouts at the outlet and the point of connection of the fixture. Autoflushers, installed in the hot water system, further decrease water age.