This incline is called the slope . Subterranean waters can remain stored for long periods or they can be moving. The rocks found under the ground surface can be permeable or impermeable . They are permeable if they quickly absorb the water that penetrates the ground. They are impermeable if they impede the passage of water, that is, they stop the filtration.
Permeable rocks absorb the rainwater, and little by little they get filled up.
Once they are completely filled, we say that they are saturated. The saturated permeable rocks form the phreatic layer . The subterranean waters are stored in aquifers, as the layer is commonly called. For this, underneath the porous rocks they have a lower layer of impermeable rocks that impede the passage of water, stopping it and helping it to be stored. Fresh water is found in rivers, lakes, ponds, in subterranean waters, and in the atmosphere.