Framework for the Statistical Characterization of Supplied Water Age in Water Distribution Networks

Water age or time of residence is frequently adopted as surrogate indicator for water quality in water distribution networks. High water ages, which are expected in terminal branches and meshed areas with low renovation rates, are associated with different physical, chemical and/or biological issues. However, the identification of critical areas is complex because it depends on the system design and associated demands, which are stochastic in nature. This work aims to develop a methodological framework to statistically characterize water age in water distribution networks. A detailed analysis of residence times is here performed at a parametric terminal branch inspired in a real case study. Water age statistical properties (mean and variance) are computed in this work from Monte Carlo simulations and compared for different network sizes, types of nodes and demand allocation strategies. Moreover, volumetric probabilistic curves for the Supplied Water AGE (SWAGE plots) are here defined and generated at each node. The practical interest of SWAGE plots (which provide the ratio of supplied water volumes with age above different threshold values) for the identification of critical areas justifies the necessity of defining a systematic framework for the STATistical characterization of Water AGE (STATWAGE). The potential and difficulties associated with the real implementation of STATWAGE are here discussed.