*Corresponding author. Development and validation of system design principles for water reuse systems D. Joksimovic a *, D.A. Savic a , G.A. Walters a , D. Bixio b , K. Katsoufidou c , S.G. Yiantsios c a Centre for Water Systems, Department of Engineering, School of Engineering, Computer Science and Mathematics, University of Exeter, Exeter, EX4 4QF, United Kingdom Tel. +44 (1392) 263730; Fax +44 (1392) 217965; email: D.Joksimovic@exeter.ac.uk b Aquafin NV, Dijkstraat 8, Aartselaar 2630, Belgium c Centre for Research and Technology Hellas, Chemical Process Engineering Research Institute, Charilaou-Thermi Road, P.O. Box 361, GR570 01, Thermi, Thessaloniki, Greece Received 1 February 2006; accepted 3 April 2006 Abstract Decision support software (DSS) for Water Treatment for Reuse with Network Distribution (WTRNet) has been developed within the AQUAREC project on “Integrated Concepts for Reuse of Upgraded Wastewater”, under the Fifth European Community Framework Programme. The overall objective of work conducted as part of the AQUAREC project has been the development and validation of system design principles for water reuse systems. The DSS provides an integrated framework for optimisation of treatment and distribution aspects of water reuse and the selection of end-users, and has been used in the development of the design principles. The principle components of the software (simulation and optimisation models) are presented, followed by the discussion on the software validation. A case study is then illustrated, on which WTRNet has been applied to develop least-cost design alternatives. Design principles for water reuse systems that were achieved by applying the WTRNet tool are presented, in which the importance of utilising formal optimisation in determining the most promising design alternatives is demonstrated. Keywords: Decision support; Least cost design; Optimisation; Water reuse Desalination 218 (2008) 142–153 0011-9164/08/$– See front matter © 2008 Published by Elsevier B.V. Presented at AQUAREC 2006 — Integrated Concepts for Reuse of Upgraded Wastewater, Barcelona, 1–3 February 2006 doi:10.1016/j.desal.2006.04.091