Groundwater is more than a resource. It is an important feature of the natural environment；it leads to environmental problems, and may in some cases offer a medium for environmental solutions. It is part of the hydrologic cycle，and an understanding of its role in this cycle is mandatory if integrated analyses are to be promoted in the context，groundwater contributes to such geotechnical problem as slope stability and land subsidence. Groundwater is also a key to understanding a wide variety of geological processes，among them the generation of earthquakes, the migration and accumulation of petroleum.