The ability of a medium to pass a fluid under pressure. Permeability exists usually in pure water that is also considered as pure water flux and characterized as the water volume that flows through membranes at per unit time, unit, and area of transmembrane pressure. One of the best examples of permeability is the cell membrane. Since permeability is influenced by hard objects such as rocks, high permeability permits the flow of fluids to transition quickly through these objects.