The water problem in Gaza Strip in Palestine is complicated; in reason of consumed water exceed the renewable water and high population density. The water situation is very important for mangers that are responsible of distribution, operation and maintenance of water networks to build an effective and complete comprehensive management of water distribution networks system. The main aim of this research is to study and evaluate the existing operation & maintenance system which is applied in Rafah area in Gaza strip which selected as pilot study area. The proposed system deals with a huge quantity of data which is needed to propose an effective system that can save time, cost, and minimize the mistakes in managing operation & maintenance systems for water distribution networks, Geographic Information System Technology is selected as one of tool decision which deals with such quantity of data and can be linked with other software which can achieve the aim of this study. The research depended on the use of Arc GIS 9.3 datasets and Water CAD/WaterGEMS hydraulic modeling based on Decision Support System for proposed water distribution plan systems, proposed operation & maintenance systems, and use pipe condition index to assist operation & maintenance manager to take the best decision which saving time, effort, and cost.