by Trayle Kulshan

Created on: April 10, 2010

An aquifer is defined as “a geologic unit which can store and supply significant quantities of water,” but that may not mean a lot to you unless you are a hydrogeologist. A simpler definition is anyplace underground which holds enough water to be useful. This article will provide a quick breakdown of what is and what is not an aquifer, give examples of different types of aquifers, and point you to some resources where you can learn more about the important natural resource called underground water.

Let's start by breaking down the hydrogeologist’s definition of an aquifer. A “geologic unit” is the ground upon which you are standing and everything underneath. It can be made of solid rocks, loose particles like sand or clays, or anything in between; even dirt is a geologic unit.

The second important part of the definition above is the term “significant” quantities of water. Significant to whom? Significant to people, of course! To be called an aquifer, the underground materials must provide enough water to be of use to people.

Water is stored within the small spaces between particles of sand and other sediments or within rocks (these spaces are called “pores”), as well as within the cracks or fractures in solid rocks. In an aquifer there are many pores or fractures connected together such that a lot of water is stored there. When people dig or drill a well into an aquifer, water flows into the hole and is easily pumped out for use.

In some cases, like in clays, water may be stored in the material, but the material is so tight or the pores are not connected such that it is impossible to pump the water out. This is called an aquiclude.

Aquifers are an important part of the hydrologic cycle. Fresh water evaporates from oceans, forms clouds which then produce rain. When rain falls onto the ground it either runs off into rivers or streams and finally to lakes or back to the oceans. But a lot of water also seeps into the ground, where it is then called groundwater.

Rivers, lakes, oceans and any other water bodies that we can see (that are above ground) are not aquifers. They hold surface water. Aquifers hold groundwater, and are always underground. Eventually, water may reach the end of an aquifer, for example on the side of a hill, where it flows out into a spring, at which point it is again called surface water.

Just like surface water, groundwater flows and moves around in the pores and fractures of the earth,

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