Water content or moisture content is the quantity of water contained in a material, such as soil (called soil moisture), rock, ceramics, fruit, or wood. Water content is used in a wide range of scientific and technical areas, and is expressed as a ratio, which can range from 0 (completely dry) to the value of the materials' porosity at saturation. It can be given on a volumetric or mass (gravimetric) basis.
One of the properties of microwaves is the ability to travel through non conductive materials.In materials with bipolar molecular structure, (i.e. water), the electric field of microwaves can induce oscillations whilst travelling through the medium. During this process, the micro waves lose some of their energy.
This loss in energy increase with the amount of water that medium contains, with the result that as the water concentration increase, less energy will reach the other side of the medium. Water not only absorbs but also reflects some of the micro wave energy. By utilizing these two effects (reflection and absorption) one is able to perform moisture measurements with micro wave techniques.