Most people think of groundwater flow as being like an underground pipe, but this is not the case at all. In reality, groundwater seeps slowly through natural gaps between the grains of sedimentary gravels or fractures in rocks.
However, not all groundwater is considered to be an aquifer. Only groundwater which exists in sufficient quantities to be useful constitutes an aquifer.
Just like a mineral deposit, unless it is economically viable to extract the water, it is not classed as an aquifer.
A distinction is made between water in the soil layer, and true groundwater, which occurs in the saturated zone below the water table. The unsaturated soil zone is also known as the vadose zone. This division is illustrated below.
Aquifers perform two very important functions. Firstly, they store water, and secondly, they transmit water. If there aren't enough gaps or pore spaces in the geological formation of an area, or if they aren't linked up, then it may not be an aquifer.
The photograph shows cemented material at Riverlands, which forms the Wither Hills. It is too cemented to form an aquifer.