Drainage is the process of water flowing away from a place, or the system that makes this happen. After a heavy rainstorm, you can watch drainage in action as water runs down your street toward storm drains, following the slope of the pavement. Without good drainage, water would pool everywhere, turning yards into swamps and streets into ponds.

Cities need carefully planned drainage systems with underground pipes, gutters, and sewers to move rainwater away from buildings and roads. Farmers dig drainage ditches in their fields to prevent crops from drowning in standing water. Even your kitchen sink has a drainage system: pipes that carry dirty water away when you pull the plug.

The ground itself provides natural drainage when soil absorbs water and lets it seep down through layers of earth. Sandy soil has excellent drainage because water flows through it quickly, while clay soil has poor drainage and holds water longer. Gardeners pay close attention to drainage because different plants need different amounts of water around their roots.

When something has good drainage, water flows away efficiently. Poor drainage means water sits too long, which can damage foundations, kill plants, or create mosquito breeding grounds.