Answer in brief :
Which part of soil water is available to plants for absorption by roots?
Capillary water is a part of soil water which is available to plants for absorption by roots. After the gravitational water has drained down, a large amount of water is retained in minute interstitial spaces in the form of thin films surrounding the soil particles which is known as capillary water. It is held in the soil against the forces of gravity and is the source of almost all the water that a plant absorbs from the soil.