This work aims to solve the water distribution network design problem presented by the Battle of the Water Networks II (BWN II) design competition. A simulation-optimization framework was developed to run on high-performance computing (HPC) platforms, and it was used to develop solutions to the network expansion design problem. The simulation-optimization framework consists of a water distribution system simulator, EPANET, coupled with population-based metaheuristic methods, such as evolutionary algorithms. The optimization method is augmented by pre-screening and post-screening of solutions based on engineering judgement. These methods were used to explore the decision space as well as the objective space for the problem in a preliminary fashion. The number of EPANET simulations in a population-based search is expected to be large and computationally demanding. Our framework allows multiple simulations to be run in parallel on HPC platforms and reduce the time required to converge to a solution. Future work will explore specialized algorithmic operators to maintain solution diversity for more efficient exploration, which is expected to improve the overall search performance, alternative optimization methods, and improvements to the parallel implementation. New methods and operators will be compared based on the search performance as well as computational requirements.