What term describes the measure of the amount of water held by a rock or soil in pores or voids, expressed as a percentage of total volume?

Porosity refers to the volume of voids or spaces within a material, such as rock or soil, expressed as a percentage of the total volume of that material. This measure is crucial in fields such as hydrology and soil science because it indicates how much water a particular substrate can potentially hold. High porosity means that there are many spaces available for water storage, while low porosity indicates that the material is more solid with fewer voids. Understanding porosity is fundamental for assessing groundwater storage, movement, and the general behavior of soils in environmental contexts.

Permeability, on the other hand, relates to the ability of a material to transmit fluids and is influenced by both the size and connectivity of its pores, but does not specifically measure the amount of water held. Specific retention measures the water that can be retained against gravity in a soil but does not encompass the total volume of voids. Specific gravity pertains to the density of a substance compared to the density of water and is unrelated to pore space and water storage capacity in soils or rocks.