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Pore Water

Pore water diagram
Idealized microscopic cross section of sediment. In three-dimensions all of the pore spaces are connected. (Not to scale)


Pore Water, or Interstitial Water - "Subsurface water in an interstice, or pore (Bates and Jackson, 1984)." - U.S. Geological Survey, 2009a

Pore Water - "Sediment interstitial water, or pore water, is defined as the water occupying the spaces between sediment particles ... Contaminants in the interstitial water and in the solid phase are expected to be at thermodynamic equilibrium. This makes interstitial waters useful for assessing contaminant levels and associated toxicity." - U.S. Environmental Protection Agency, 2001

Interstitial Water - "Water occurring in the small openings, spaces, and voids between particles of unconsolidated materials in that portion of the vadose water zone between the roof zone and the water table. The water is held in place by entrapment, ionic attraction, and capillary or adhesive forces, rather than from upward pressure components of saturation." - U.S. Geological Survey, 2006

Pore Water - "The rocks that form the crust of the earth are in few places, if anywhere, solid throughout. They contain numerous open spaces, called voids or interstices [pores], and these spaces are the receptacles that hold the water that is found below the surface of the land and is recovered in part through springs and wells." - Meinzer, 1923

Related Definitions

Sediment - "Sediment is detached fragmental matter that originates from either chemical or physical weathering of rocks and minerals and is transported by, suspended in, or deposited by water or air or is accumulated in beds by other natural agencies." - Osterkamp, 2008

Interstice - "(1) An opening in a rock or soil that is not occupied by solid matter (AGI, 1980). (2) An opening or space which may be occupied by air, water, or other gaseous or liquid material (ASTM, 1980). Synonymous with void, pore." - U.S. Geological Survey, 2009b

Porosity - "The ratio of openings (voids) [pores] to the total volume of a soil or rock ... Porosity is expressed either as a decimal fraction or as a percentage." - Heath, 1983

Porosity - "The porosity of a rock is its property of containing interstices. Some authors have used the term to refer only to minute interstices, which they call pores, but in comparison with the size of the earth itself even the largest openings are no more than pores, and the term 'porosity' is much more useful if it is made to apply to all openings having an arbitrary limit of size. Porosity is expressed quantitatively as the percentage of the total volume of the rock that is occupied by interstices or that is not occupied by solid rock material. A rock is said to be saturated when all its interstices are filled with water. In a saturated rock the porosity is practically the percentage of the total volume of the rock that is occupied by water." - Meinzer, 1923

Unsaturated Zone

Text in brackets ("[text]") are additions by the editor.

USGS Information

  • Search the Toxic Substances Hydrology Program's Bibliography for "pore water"

Related Science Feature Articles


American Geological Institute, 1980, Glossary of geology: Falls Church, Virginia, American Geological Institute, 751 p.

American Society for Testing and Materials, 1980, Standard definitions of terms and symbols relating to soil and rock mechanics, in Annual Book of ASTM Standards, Part 19: Philadelphia, Pennsylvania, American Society for Testing Materials, p. 1402-1419.

Bates, R.L., and Jackson, J.A., 1984, Dictionary of geological terms: New York City, NY, American Geological Institute, 571 p.

Heath, R.C., 1983, Basic ground-water hydrology: U.S. Geological Survey Water-Supply Paper 2220, 86 p.

Meinzer, O.E., 1923, The occurence of ground water in the United States: U.S. Geological Survey Water-Supply Paper 489, 321 p.

Osterkamp, W.R., 2008, Annotated definitions of selected geomorphic terms and related terms of hydrology, sedimentology, soil science and ecology: U.S. Geological Survey Open-File Report 2008-1217, 49 p.

U.S. Environmental Protection Agency, 2001, Collection of interstitial water, in Methods for collection, storage and manipulation of sediments for chemical and toxicological analyses--Technical manual: U.S. Environmental Protection Agency, Washington, D.C., Office of Science and Technology, 208 p.

U.S. Geological Survey, 2006, Appendix A--Codes used in water-quality processing system, in User's manual for the National Water Information System of the U.S. Geological Survey: Reston, Virginia, Open-File Report 2006-1145, 381 p.

U.S. Geological Survey, 2009a, Lanslide hazards program glossary: U.S. Geological Survey, access date June 21, 2011.

U.S. Geological Survey, 2009b, Glossary of hydrologic terms: U.S. Geological Survey, Oregon Water Science Center, access date June 21, 2011.


Disclaimer: The definitions on this page are provided for information purposes only, and do not indicate endorment by the U.S. Geological Survey.

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