Drainage, in agriculture, is the removal of excess water that is on or beneath the surface of the soil. Most plants do not grow well in soil that is saturated with water. Usually, water drains naturally from the soil. The water runs off, evaporates, is absorbed by the soil, or used by plants. In areas that do not drain naturally, artificial drainage systems may be used to aid plant growth. Drainage systems are also used to make soil suitable for other purposes, including the construction of buildings and highways.