A ballcock is a mechanical device used in toilets to control the flow of water into the tank. It consists of a float, usually shaped like a ball, that rises and falls with the water level. When the tank is empty, the float drops, opening a valve to allow water to fill the tank. Once the water reaches a certain level, the float rises and closes the valve, stopping the flow. Ballcocks are essential for the proper functioning of toilets, ensuring they refill after each flush. They can be found in various types of toilets, including those with gravity-fed and pressure-assisted systems. Regular maintenance of the ballcock can prevent leaks and ensure efficient operation.