Residual Chlorine and Water Age Analysis in Optimal Water Distribution System Designs

Water Distribution Networks (WDS) for drinking water have long been (and continue to be) a crucial challenge to society’s development. Systems to meet this need can have infinite configurations to achieve the same goal for a given city. Using optimization methodologies and heuristics it is possible to get the least cost design out of those alternatives. However, cost is not the only variable to consider in a given design. Water quality, measured using residual chlorine and water age among other hydraulic characteristics, must comply with local regulations. A correlation between the minimum cost design of a given WDS and higher water quality characteristics has been identified in the past, because the optimal network tends to have the minimum water volume inside and therefore high velocities resulting in least water age and higher average residual chlorine for given bulk and wall decay coefficients. This is a consequence of the form of minimum cost equation for pipes and excavation. In this research work 10 benchmark networks were studied to prove that hypothesis. First, they were designed using the Optimal Power Use Surface (OPUS) methodology, which gives a near optimal design. Then, four different non-optimal designs were calculated for each one of the benchmarks. Last, using EPANET software, average residual chlorine and water age were carried out and compared among all alternatives. Results showed that WDS minimum cost designs always have the least water volume, the least water age and the higher residual chlorine concentrations.