Water below the surface of the Earth stored in pore spaces and fractures within rock or layers of sand and gravel. (See Aquifer); In water resources management, the term specifically applies to water that can be extracted sufficiently easily at sufficient quantity for our needs and quality for human use (with or without treatment). Saline water or water contained in rocks of very low permeability is not conventionally considered groundwater although some use the term to include all underground waters.
Surface water and groundwater commonly interact with water flowing between them in either direction (sometimes carrying pollution). In other situations they are separated, for example by an impermeable clay base to a canal or lake.
See Surface water
