In the last three decades, the need of achieving a reliable water distribution system has become more eminent for both the consumer’s satisfaction and the efficient management of water sources. The purpose of this paper is to provide an optimal separation of a water distribution network (WDN) into District Metered Areas (DMAs) in order to ensure that the delivered water is of proper age and pressure. At first, the water distribution network is divided into smaller areas via the method of Geometric Partitioning, which is based on Recursive Coordinate Bisection (RCB). Subsequently, Gaussian Mixture Modelling (GMM) solution is applied, obtaining an optimal placement of isolation valves and separation of the WDN into DMAs. The performance of the proposed system is evaluated on two different networks and is compared against the Genetic Algorithm (GA) tool, constituting a very promising approach, especially for sizeable water distribution networks due to the diminished running time and the noteworthy reduction of pressure and water age.