The higher the porosity, generally, the more stored groundwater. Primary porosity refers to that which developed when the rock formed. Secondary porosity develops after the rock is formed. Primary porosity is usually higher in sedimentary rocks and lower in igneous rocks. It can be high in volcanic rocks, however.
Porosity generally decreases with depth.
The deepest drillhole on earth, the Kola Hole in Siberia, at a depth of 12km did have water-filled fissures. Aquiclude - a confining rock layer with low permeability. A karst aquifer in Edwards limestone which is highly permeable, even cavernous. Read text, p.248. Catfish farmer tapped in and drew out one-half of the aquifer's water.