A line that is connected to a continuous water supply is referred to as what type of line?

The term that best describes a line connected to a continuous water supply is a regular line. This designation indicates that the line is intended for firefighting purposes and is dependable for sustained water supply during an incident. Regular lines are critical in ensuring that firefighters can effectively combat fires without interruption due to lack of water.

The other terms relate to different types of operational lines but do not accurately denote a line specifically connected to a continuous supply. For example, a backup line may refer to an additional hose line ready to be deployed if the primary line fails. An attack line is specifically meant for direct engagement with the fire, typically involving a smaller diameter line that allows for easier maneuverability. A relief line is usually established to support or supply additional water to the operating lines in firefighting operations, but not necessarily a direct connection to a continuous water source.

Thus, regular line is the most appropriate term in this context, as it implies a reliable and continuous water supply for firefighting efforts.