ABSTRACT
The void space provides a place where groundwater can be stored and kept under suitable conditions for use at times of demand. The most important and commonly known reservoirs are composed of granular materials such as unconsolidated and consolidated sands. In general, only the sedimentary rocks of different origins provide porous media for groundwater occurrence and movement. In arid regions, they reach dimensions larger than in humid regions and play a more important role as potential aquifers. In general, the groundwater of the world is derived from several sources. Most of the groundwater is derived from the atmosphere in the form of rainfall, snow, hail, humidity. Water of this type is referred to as meteoric water. Aquifers can be classified according to prevailing subsurface geological composition, or to hydrological conditions, or to groundwater pressure. Groundwater storage results from the various hydrological and geological events that occur throughout geological time.
