The Rule Based Expert Systems (RBES) constitute a powerful tool to support the decision making procedures in cases where there is not the desirable degree of structure (unstructured or semi-structure) stemming from the fact that the problem of decision-making is complex or there is no formed decision or there is no step-by-step procedure that can be used to support the Decision Maker effectively. This paper presents a real world case study regarding the management of the water supply meters network, which constitutes an unstructured problem of decision-making. The application of a Rule Base Expert System encapsulating knowledge obtained from the data analysis of the Consumer Recording system as well as from the expression of expert knowledge was an efficient solution in determining the meters suspected of under-recording water consumption as well the degree of under-measurement. Finally this research work concludes with the design of a schedule for the replacement and maintenance of the water consumption meters. The system NeMO (Network Measurement Optimisation), a Rule Based Expert Systems, was developed for this Decision Problem with the aim of providing both a cost-effective way and an efficient tool to improve the precise accuracy of water measurement and the relative positive results for the water supply organization.