Water supply in plants is due to Osmosis.

Explanation:
Osmosis is the movement of water molecules from a region of higher water concentration to a region of lower water concentration through a semi-permeable membrane. Plants absorb water through their roots by the process of osmosis. The root hairs of plants have a higher concentration of solutes than the soil water, which creates a concentration gradient, allowing water to move from an area of higher concentration (soil water) to an area of lower concentration (root hairs). This process helps in the absorption of water and essential minerals by the plant.

Other processes involved in water supply in plants are:
Imbibition: It is the process by which the plant absorbs water through direct contact with the cell walls. This process is important in the germination of seeds and the uptake of water by dry plant tissues.

Guttation: It is the exudation of water droplets from the tips or edges of leaves of herbaceous plants. This process occurs when the rate of water absorption by roots is higher than the rate of transpiration, leading to the accumulation of water in the plant.

Adhesion force: It is the force of attraction between water molecules and the surface of the root hairs. This force helps in the movement of water from the soil to the root hairs by overcoming the force of gravity.

However, the primary process involved in water supply in plants is osmosis.