Groundwater is water below ground surface that fills the pores and cracks in both sediments and rocks.
Groundwater in sediments and bedrock. (Illust. Alf Næsheim/Steinar Skjeseth)The top surface of groundwater is called the water table, which is defined as the surface where groundwater pressure is equal to the atmospheric pressure.
The water table in bedrock is not a continuous surface because groundwater is mainly confined to cracks and cavities. In the groundwater zone below the water table, all pores and cavities will be completely filled with water, and this zone is therefore also referred to as the saturated zone.
Between the water table and the ground surface, in the so called unsaturated zone, pores are partially filled with air while water adheres to the surface of sediment grains or minerals in rock.
Groundwater comprises globally 95 % of all liquid fresh water on earth. Thus, groundwater is the main source of drinking water in several countries. In Norway the dominant resource of groundwater occurs in unconsolidated sediments.
The amount of groundwater at any time and place will be dependant on climate and ground conditions. The climate determines the amount of water available for precipitation and evaporation, while the ground properties determine whether water can infiltrate in the subsurface to replenish the groundwater reservoir. If evaporation in an area is larger than the amount of precipitation, there will be no new formation of groundwater and the water table will be located deep below the surface.
Do you want to know more about groundwater?
The Groundwater Section at NGU runs a separate website, www.grunnvann.no, containing both general knowledge and specific information about Groundwater in Norway. There you can find more detailed information about quality, use and management of groundwater, research, databases, and other sources of information.
Published: 24. January 2008