A ball valve is a quarter-turn valve which uses a pivoting ball with a hole to control flow through it. When the ball’s hole is in line with the flow then it is open and water flows through. When pivoted 90-degrees the water is closed. It is easy to tell when the valve is open, the handle of a ball valve should be in alignment with the flow when open or perpendicular to it when closed.
Ball valves are durable and reliable, and will close securely even if they haven’t been used for a while. These qualities make them an excellent choice for rainwater tanks.