Optimizing the Sustainability of Water Distribution Systems

Recent research has emphasised the need to consider sustainability as a key objective of water supply systems. In a previous publication, the principal author presented a methodology for considering the total energy of a water distribution system (WDS) as an effective measure of the sustainability of the system. The total energy (including embodied energy of the materials as well as the energy consumed in the operation of the system) is closely related to the greenhouse gas emissions associated with the system. Most optimization studies of WDS have optimized a single objective such as capital cost or the net present value (NPV) of capital plus operating cost. A few multi-objective studies have been carried out previously but few have effectively considered sustainability objectives. In this study, a multi-objective genetic algorithm was used to identify the Pareto optimal trade-off between cost and total energy for a simple WDS. This technique does not identify a single "optimum" design but rather a set of technically efficient solutions each of which places a different relative weight on the two objectives of cost and total energy. The results for the test WDS demonstrate that different designs are obtained when minimizing the total energy of the system compared to minimizing cost alone. There are also compromise solutions between these two extremes. The methodology presented represents an advance in the consideration of sustainability in the design of WDS.