This study presents comparative life cycle assessments (LCAs) and levelised cost (LC) analyses of desalination supply systems, integrated with a spatial-temporal model at three geographical scales: a centralised scenario and two alternative decentralised scenarios. For the centralised scenario we focused on a proposed 320,000 m(3)/day SWRO desalination plant to support future urban expansion in the northern corridor of Perth, Western Australia. The alternative, decentralised scenarios each integrate several medium sized plants into the same geographical water demand area as the centralised scenario and also produce 320,000 m(3)/day in total. Results indicate that environmental impacts would be similar to 20% lower and LC 7% to 18% lower for the decentralised scenarios than for the centralised scenario. Contribution analysis revealed that, for the centralised scenario, although economies of scale resulted in lower environmental impacts from the desalination plant construction and operation phases, these savings were outweighed by the environmental impacts associated with the construction and operation of the water transfer mains required to connect the large plant to the network. Perth water stakeholders and policy makers can use our results to inform development decisions, and the proposed LCA method can be implemented in other metropolitan areas for desalination planning. (C) 2015 Elsevier B.V. All rights reserved.