Aquifer is a term used in geology to define underground geological structures that, being totally saturated, are suitable for the storage and transmission of water in abundance. It is characterized by presenting an important permeability, extension and thickness. These geological formations, by allowing the movement of water through their cracks, allow humans to take advantage of it to satisfy their needs.
These bodies of water can be found stored within a surrounding rock, in this case we would be talking about a confined aquifer; or be within a layer of water filled with sand, which is called an unconfined aquifer. These two types of aquifers are used by man for irrigation, consumption and industrial applications.
From the hydraulic point of view there are four classes of aquifers:
Free aquifers: are those where the surface is free of impervious formations, since the water contained in them is at atmospheric pressure.
Confined aquifers: are those that are lined by an impermeable surface. The water contained is at a pressure greater than atmospheric. When a well is drilled in this class of aquifers, the water rises through it, until it reaches a height called the piezometric level.
Semi-confined aquifers: are those where the water is at the same pressure as the confined ones, with the difference that in this case, the layers that confine it are not completely waterproof and allow small leaks that affect the flow extracted from the aquifer semi-confined.
Coastal aquifers: they are those that can be free, confined and semi-confined, however the characteristic that distinguishes them is the presence of two fluids with different densities: fresh water with a lower concentration and salt water with a higher density.
These types of formations originate as a consequence of rainwater that falls to the earth's surface and is absorbed by it, allowing the water to permeate the ground, which, being permeable, causes the water to form underground layers. This water will form layers until it reaches an area where the rock formation is impermeable and where the water will be stored, forming an aquifer.
Aquifers today represent one of the world's largest reserves of drinking water in the future, therefore it is vital that man try not to pollute them, especially unconfined aquifers, since they are the ones that are most exposed to contamination from of cities (canals, drains, etc.)
