How Stuff Works explains that water reaches the leaves of plants through the xylem vessels, and it escapes through small holes in the leaf known as stomata. The process by which the water moves from the capillaries to the xylem vessels and into the stomata is called transpiration. Plants absorb water through their roots, which contain capillaries. The capillaries are responsible for sending water through the xylem vessels.
According to the BBC, many plants contain 90 to 95 percent water. Since plants are made up of mostly water, they are dependent on it to stay alive. Water is responsible for the regulation of temperature in plants and for the transportation of nutrients throughout the plant. Plants receive water from rainfall, dew and natural and man-made irrigation systems in order to survive.
Green plants use water for photosynthesis. Photosynthesis allows plants to produce the sugar which they need for food. Plants are also dependent on water to support their physical structures. During the process of osmosis, which is the movement of water from the outside of a plant's cells to the inside of the cells, the plant's cell wall receives the structural support that it requires, according to How Stuff Works.