In this paper, a mixed scenario-based and probabilistic two-stage stochastic programming model is proposed for the design of integrated water supply and wastewater collection systems. None of the existing models simultaneously takes into account both business-as-usual and hazard uncertainties. To explore suitable solutions in a reasonable time, a solving procedure comprised of the (1) sample average approximation method, (2) Bezdek fuzzy clustering method and (3) Benders decomposition algorithm is developed. In order to expedite the convergence of the applied Benders decomposition algorithm, different acceleration techniques especially the local branching method are utilized. The performance of the proposed mathematical model and solution procedure is analyzed computationally through a real case study which the results show the usefulness of the developed stochastic programming model as well as the efficiency of the solution approach. (C) 2017 Elsevier Ltd. All rights reserved.