What does porosity measure in relation to rocks and water?

The concept of porosity fundamentally relates to the amount of void space within a material, specifically rocks in this context. It quantifies how much of the rock is made up of spaces that can hold fluids, such as water. Thus, when we talk about porosity, we are focusing on the proportion of the rock's volume that consists of these open spaces or pores relative to the total volume, which is expressed as a percentage.

The correct answer specifically defines porosity as the amount of water that can be held in the pores of the rock, thereby directly addressing what porosity measures. High porosity indicates that a greater volume of water can be stored in the rock, which is crucial for understanding groundwater aquifers and other geohydrological systems.

When evaluating related concepts like permeability and specific yield, these terms involve different aspects of water movement and storage rather than simply measuring void space. Therefore, it's important to recognize that while they are interconnected in relation to water flow through geological formations, porosity itself is specifically concerned with the capacity of the rock to hold water.