Hygroscopic water is defined as the

• 1) Gravitational water:
-When water is added to the soil during irrigation, the soil content is raised to a saturation level, at this point, the pores are completely filled with water and the soil contains the maximum possible water content.
-Which thus, consists of the upper limit of gravitational water.
-It is the water that is not held by soil but drains out freely under the influence of gravity.

• 2) Capillary water:
-It is that water that is retained in the soil after the gravitational water has drained off from the soil.
-Capillary water is held in the soil by surface tension, as a continuous film around the soil particles and in the capillary pores between the soil particles.
-It is also known as available water.
3) Hygroscopic water: 
-It is the water which is absorbed by the particles of dry soil from the atmosphere and is held as a very thin film on the surface of the soil due to adhesion or attraction between the surface of particle and water molecules.
-Below the permanent wilting point, the soil only contains hygroscopic water.
-In general, it is not available for the use of plants.