Most water supply infrastructures were established during India's independence period and some oil pipelines are more than 70 years old. Aging and uncertainty about its performance under the growing and varied pattern of demand puts tremendous pressure on water authorities to rehabilitate the existing system for the complete renewal of the system. Complete renovation not only increases the cost to the water authority, but also causes potential inconvenience to the consumer in terms of getting a new connection with new line. Therefore, it is essential to rehabilitate pipelines that are most sensitive in the local service. Rehabilitating the existing system is usually done by replacing existing pipes with the same diameter or more or by placing the pipe parallel to the existing pipe. The optimal selection of such a combination is a furious task for water authorities. In the present study, a combined simulation-optimization model is developed using the EPANET simulation engine. The differential evolution algorithm is adopted to arrive at the optimal solution.