Hydrogeology studies underground water, its origin, movement, distribution under Earth’s surface and conservation.

Underground water is that found under the soil’s surface in the saturation area (subsoil layer in which the pores or interstices are flooded with water) and form part of the water’s global lifecycle in Earth.

Underground water in this area moves, generally speaking, very slowly (a few centimetres to a few metres per day) based on three phenomena: gravitational action, molecular attraction and density differences, the latter resulting in turn from temperature differences found in water.

Is in this slow travel where water gathers in dissolution all those elements found on its way, which depending on the relevant features (ph, mineralization, temperature) as well as on the rock it may dissolve. As a result, underground water initially coming from rainfall and nearly free from elements in dissolution, will be progressively enriched with such minerals characteristic of the rocks comprising the aquifer. Thus, for instance, a karstic aquifer will produce underground water rich in calcium and magnesium bicarbonates.