The correct answer is - permeability.
The permeability is the substance's ability to allow another substance pass through it, which in this case would be the water through the rocks.
The unit used for the measuring of the permeability is milidarcies, at least most of the time.
The permeability is directly connected to the porosity of a rock. The more porous a rock is, the bigger the permeability, and the less porous a rock is, the lesser the permeability.
Through this process, the water is able to penetrate deep inside the rocks and into the ground. That results in the creation of water reservoirs from which the springs emerge when they are full and the water is able to come to the surface, or reservoirs of groundwater.
