The effects of gravity. Where a stream, lake or swamp is found, the water table coincides with the surface of the body of water. Factors Influencing the Storage and Movement of Groundwater Rock and sediment contain voids called pore spaces. The porosity is the percentage of the total volume of rock that consists of pore spaces. The quantity of water that can be stored depends on the porosity.
Different rocks have different porosities.
Rocks may have very high porosities but not let water move through them. The permeability of rock is its ability to transmit water. Depends on porosity and interconnectedness. Molecular attraction or surface tension inhibits flow particularly in small pore spaces. Aquifers are rocks with high permeability.