Porosity is the amount of empty space in a rock or other earth material (like sand) - in other words, it's how much water a material can hold.
Permeability refers to how well water flows through a material - the flow is controlled by how large the pores are and how well connected the pores are in a given object.Therefore, there these are two primary factors that limit the movement and the amount of water (or other fluids) retained in rocks/sedimentary materials.