Water content means the amount of water present in a porous substance, such as soil. This term is used in hydrogeology, soil science and soil mechanics. In saturated groundwater aquifers, all available spaces are filled with water. Above a capillary fringe, pore spaces have air in them too.
Gaps between soil particles are called pore spaces or voids. These voids contain various amounts of either water or air. Soil moisture content can be expressed in different basis:
- Gravimetric: the mass of water/mass of solid material
- Volumetric: the volume of soil/total porosity
The amount of void space within a soil depends on the distribution of particle sizes, and is quantified by soil porosity.
Soil moisture is more generally considered within the context of hydrology, where it represents the immediate store of infiltrating rainfall, before it either evapotranspires or contributes to groundwater recharge.