The type of rock that works best as an aquifer is volcanic rock that fills in as rubble between flows. This type of rock is highly porous and rather permeable, permitting significant water movement.
Other types of rock that work as aquifers include columnar basalt, sandstone, unconsolidated sand and gravel, conglomerate and fractured limestone. Generally, any kind of fractured rock layer works well as an aquifer which is defined as a body of saturated rock which water moves through.
Rock types like granite and schist, which have low porosity, are not good aquifers. Porosity measures the ability of water to move through the rock layer, while permeability indicates how water moves into that layer from others.