Design of Integrated Water Systems: Water Distribution System, Household Water-Saving Scheme, and Sanitary Sewer Perspectives

Abstract

An integrated design method that complements the increasing uptake of water-saving schemes (WSSs) is presented. WSSs may consist of water-saving fittings, appliances, rainwater-harvesting systems (RWHSs), and water-reuse schemes that provide the link between water distribution systems (WDSs) and sanitary sewers (SSs). The method developed here considers the interaction between WDSs, WSSs, and SSs to provide unified solutions. In this paper, a multiobjective optimization problem is formulated and solved considering three objectives, which are (1) minimization of the total cost incurred by implementing water system interventions, i.e., excluding the associated cost savings; (2) maximization of cost savings, which are benefits conferred by interventions; and (3) minimization of system water demand. The decision variables include conventional water network design interventions (i.e., addition of pipes) and the water-saving equipment at a household level. The main constraints include both WDS and SS hydraulic performances. The optimal trade-off solutions are obtained using nondominated sorting genetic algorithm optimization processes. This method was demonstrated in the realistic subsystem of the Tsholofelo Extension water and SS networks in Gaborone, Botswana. The results show that integrating and optimizing WDS, WSS, and SS designs would improve water security and lead to more sustainable water systems.