According to Herlambang (1996) groundwater is water that moves in the soil contained in the space between soil grains that seep into the soil and combine to form a layer of soil called aquifers. Layers that are easily traversed by groundwater are called permeable layers, such as layers found in sand or gravel, whereas layers that are difficult to pass through groundwater are called impermeable layers, such as clay or loam layers. The layer that can capture and escape water is called an aquifer.

In general aquifers are divided into two namely unconfined aquifer and confined aquifer. Unconfined Aquifer is a water-escaped layer which is only partially filled with water and is above a waterproof layer. The surface of the aquifer is called the water table (preatiklevel), which is a water surface that has the same hydrostatic pressure as the atmosphere. Confined Aquifer is aquifer whose entire amount of water is limited by waterproof layers, both above and below, and has a saturation pressure greater than atmospheric pressure.

Confined aquifer is formed due to the free motion of gravity so that water can enter it, whereas Unconfined aquifer is formed because there is too much water in the confined aquifer so that the water in it presses the waterproof layer so that it enters it. This waterproof report in the form of rocks where when the water in the confined aquifer breaks into this waterproof layer (the rocks) filters the water to be cleaner not only that water that breaks through the impermeable layer also brings mineral to the rocks. This is what makes unconfined aquifer water quality better than water in confined aquifer.

The process of getting water into the soil to form an aquifer takes several million years. Confined aquifers do not form as long as unconfined are formed. This is because confined aquifers are formed first before unconfined aquifers are formed.