Root hairs absorb water from the soil by osmosis.
Root hairs are slender, elongated, and tubular outgrowths that arise from the outermost layer of cells in a root known as the epidermis. They increase the surface area of the root, allowing for more efficient absorption of water and minerals from the soil.
Osmosis is the movement of water molecules from a region of higher water concentration to a region of lower water concentration across a semi-permeable membrane. In the case of root hairs, the soil water has a higher concentration of water molecules compared to the cytoplasm of the root hair cell, so water moves from the soil into the root hair by osmosis.