A systematic design methodology is developed in this work for simultaneously synthesizing the multi-contaminant water-allocation and heat exchange network (WAHEN) in any chemical process. Specifically, a modified state-space representation is adopted to capture the structural characteristics of the integrated WAHEN, and a mixed-integer nonlinear program (MINLP) is formulated accordingly to minimize the total annualized cost (TAC) of the network design. In the proposed mathematical programming model, not only all possible water reuse and treatment options are incorporated, but also the direct and indirect heat-exchange opportunities are considered as well. To enhance the solution quality and efficiency, a stochastic perturbation procedure is introduced to generate reliable initial guesses for the deterministic optimization procedures and also, an interactive iteration method is developed to guide the search toward a potential global optimum. Three examples are presented in this paper to demonstrate the validity and advantages of the proposed approach. (c) 2008 Elsevier Ltd. All rights reserved.