Relative Water Age in Premise Plumbing Systems Using an Agent-Based Modeling Framework

Tools used to predict hydraulics and water quality within premise plumbing systems have gained recent interest. An open-source Python-based tool—PPMtools—for modeling and analyzing premise plumbing systems with WNTR or EPANET is presented. A relative water age—the time water has spent in a home—study using three real-world single-family homes was used to demonstrate PPMtools. Results showed that increased use—more people or higher flow fixtures—led to a general decrease in relative water ages. However, even with more use, one user could still experience water for a drinking activity with a relative water age equal to, or longer than, the duration of the longest stagnant period (sleeping or absence from home). Simulations also showed that the general relative water ages increased if the homes were plumbed with larger diameter piping [19.1 mm ($3/4\mathrm{in.}$) versus 12.7 mm ($1/2\mathrm{in.}$)]. Hot water heaters were found to have the largest impact on relative water age. Smaller volume uses generally had more variability in relative water ages, while larger volume uses (e.g., showering) resulted in generally low relative water ages with less variability because larger uses fully replaced water in the home with water from the main. This study highlights the potential for using PPMtools to explore more complex water quality modeling within premise plumbing systems.

The time water spends (its relative age) in a premise plumbing system (home or building) provides a simple metric for estimating water quality. PPMtools was developed as a framework for simulating premise plumbing systems and was demonstrated using a water age study. PPMtools provides a tool for using EPANET to model these systems and handles fixture, activity, and agent (person or device) level information for model generation and analyzing results. This work demonstrates preliminary findings for three single-family homes with their EPANET input files and discusses their general implications. PPMtools can be used to study other premise plumbing water topics with additional work, where this work demonstrates the foundational work on PPMtools’ development. These results highlight some general trends associated with occupancy level, plumbing sizing, and the impact of low-flow fixtures, and they are discussed in terms of their impact on relative water ages. Results highlight that simplified metrics may fail to capture the full complexity of estimating water age or interuse stagnation periods.