Why does some earth materials hold more water than others?

Earth materials vary in their capacity to hold water due to differences in their porosity and permeability. Porosity refers to the amount of pore space within a material, while permeability describes how easily water can flow through it. Materials with high porosity and permeability, such as sand and gravel, can hold more water compared to materials with low porosity and permeability, such as clay and bedrock.