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Terms & Synonyms


Official WHO Definition

A geological area that produces a quantity of water from permeable rock (WHO 2006).


Materials which permit water to pass through them easily are said to be permeable and those which permit water to pass only with difficulty, or not at all, are described as impermeable. A layer of rock that is sufficiently porous to store water and permeable enough to transmit water in quantities that can be economically exploited is called an aquifer. Groundwater flow may take place through the spaces between the grains or through fissures, or by a combination of the two in, for example, a jointed sandstone or limestone. For any aquifer, distinguishing whether inter-granular or fissure flow predominates is fundamental to understanding the hydrogeology and to designing monitoring systems, particularly for point source pollution incidents (WHO et al. 1996).

Other Definitions

Where groundwater can move rapidly, such as through gravel and sandy deposits, an aquifer can form. In an aquifer, there is enough groundwater that it can be pumped to the surface and used for drinking water, irrigation, industry, or other uses.

The amount of water an aquifer can hold depends on the volume of the underground rock materials and the size and number of pores and fractures that can fill with water. An aquifer may be a few feet to several thousand feet thick, and less than a square mile or hundreds of thousands of square miles in area.

Aquifers get water from precipitation (rain and snow) that filters through the unsaturated zone. Aquifers can also receive water from surface waters like lakes and rivers. When the aquifer is full, and the water table meets the surface of the ground, water stored in the aquifer can appear at the land surface as a spring or seep.


Interpretations and Explanations


WHO (2006) Guidelines for the safe use of wastewater, excreta and greywater.

WHO/UNESCO/UNEP (1996) Water quality assessments: A guide to the use of biota, sediments and water in environmental monitoring, London, E&F Spon.

WHO Lexicon page (translations and examples)

See also

Aquifer types

External Resources

WHO/UNEP (1997) Water pollution control: A guide to the use of water quality management principles, London,E&F Spon.

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