peameable rock means that it can be permenated or penetrated, especially by liquids or gases
The zone of aeration is where there is both air and water within the pore spaces in the ground. In the zone of saturation the pore spaces are totally filled with water. The boundary between these two zones is known as the water table or phreatic surface.
Rain is not an agent of erosion but water is. Water is the major physical agent that breaks rock. H20 weakens the stenght of the rock. it depends on pemeability. Water can detroy rock also by frost wedging. When the water freezes in a rock particles and get iced up. it expands the rock and as it goes back to water reduce and a continuous process will keep digging into the rock and weather it.