An Aquifer as defined by North American Lake Management Society (NALMS):

A geologic formation, a group of formations, or a part of a formation that is water bearing. A geological formation or structure that stores or transmits water, or both, such as to wells and springs. Use of the term is usually restricted to those water-bearing structures capable of yielding water in sufficient quantity to constitute a usable supply.

Unconfined aquifers have an upper boundary defined by the water table. This means that the water level can rise or fall as the recharge (e.g. from surface precipitation and infiltration) and discharge (e.g. to lakes and rivers, or other formations) conditions change over time.

Confined aquifers are those which are bounded above and below by a low permeability confining layer, which tends to keep the water in the aquifer mostly contained. Movement is generally through the aquifer itself as opposed to up and down between layers. They tend to have relatively constant pressure heads, unless they are tapped by a well. Depending on the pressure head within the confined aquifer, the well may be artesian, meaning it can flow freely toward the surface (or even reaching the surface) without pumping required.

Aquifers can be generally classified by the type of material in which they reside. Terms such as "shallow" or "deep" aquifers, though they can be useful, do not always take into account the complex geology beneath the ground surface. Bedrock aquifers can be located near or at the surface in some places, while surficial or overburden deposits can extend to great depths, sometimes in excess of hundreds of metres. Therefore, the characteristics of aquifers (chemistry, yield, etc.) can often be generalized based on the type of deposit, and not necessarily based solely on the absolute depth.

Overburden aquifers are mainly found in the gravels and sands of pre-glacial valleys. These valleys are the buried remnants of the river systems that existed prior to glaciers carving and remoulding the landscape. The valleys are now buried under layers of glacial till, fluvial (river) sands and silts, or lacustrine (lakes) silts and clays.

Other surficial deposits that can contain aquifers are lag deposits, or outwash of sands and gravels from glacial tills, post-glacial aeolian (wind-borne) deposits, and terraced sands and gravels. Also, elevated plateaus with pre-glacial sands and gravels that are surrounded by glacial till and clay can hold substantial quantities of readily available water. These types of aquifer containing formations are commonly found in northern Alberta.

Most of the bedrock in Alberta that holds potable water is sedimentary. As mountains erode, the sediments are deposited in seas, lakes, deltas, beaches and on the land itself. As the layers build up, the immense pressures turn the sediments into sandstone, shale, siltstone and other types of sedimentary rocks. Typically sandstones are found near the foothills and shales are found in the plains and lowlands of Alberta. Sandstone is one of the more permeable forms of bedrock, and as a result, typically contains high yielding aquifers, that are suitable for our use.