The Wadi Ma'awil catchment in Barka in Eastern Batinah is known to be of great significance to the area and the nearby towns. The area population rely totally on the groundwater as the main source for life activities. Domestic, agricultural and all other uses of water depend entirely on groundwater, especially in the lower or north part of the catchment. In addition to that, the Government is looking for a strategic alternative water resource for the capital area, Muscat. Unpredicted emergencies such as any breakdown in the desalination plant that supplies domestic water to the population in Muscat, make it a necessity to look for other supplies. Constructing a water balance for the catchment is absolutely an obligation since it is the main source for consumption, hence calculate the volume and focus deeply on the dimensions and characteristics of the basin. The model used is a simple conceptual model that calculates the storage of the basin by using an equation that adds all the input and output components in the catchment to show how much is available as a surplus or as a deficit. From the calculation of the available data, it is visible that groundwater is already depleted since the Sultanate is under a drought period that has lasted for more than five years. The deficit is very drastic especially in the north catchment. The storage does not stand the consumption anymore as it is already over drafted due to the intensive agriculture that has evolved during the past three decades without strict mposed legislations.