The amount of water in a formation primarily depends on what factor?

The correct factor that primarily determines the amount of water in a formation is the porosity of the water-bearing formation. Porosity refers to the proportion of void spaces within a material, such as rock or sediment, that can hold water. A formation with high porosity contains more pores and, consequently, can store more water. This characteristic is fundamental in aquifer studies because it quantifies how much water can be retained in the subsurface materials.

In contrast, while permeability is important for the movement of water through the formation, it does not directly relate to the volume of water that the formation can hold. The depth of an aquifer may affect pressure and the availability of water, but it does not inherently dictate the storage capacity; deep formations might still have low porosity. Temperature can influence various physical properties of water, such as its density and viscosity, but it does not impact the actual amount of water that a formation can store. Therefore, understanding porosity is essential for water resource management and aquifer sustainability.