How does water pass through rock?

All rocks have a characteristic called porosity. If you imagine a jar full of golf balls, there are spaces between the golf balls. The spaces are called pores (in a geological sense). Porosity is the ratio of these spaces to the volume of the rock and can be expressed as a percentage of the total volume of the rock. In some cases pores can be interconnected allowing water to fill up the pores and pass through into the adjoining pores of the rock. In order for water to pass through a rock, it must be permeable (i.e. have interconnected pores) as well as porous.