Which term describes the pressure that is present in a water distribution system when water is not flowing?

• A. Residual pressure
• B. Static pressure
• C. Normal operating pressure
• D. Flow pressure

Answer: (A)

The pressure in a water distribution system when no water is moving is the baseline pressure in the line, since there are no losses from flow. In firefighting terminology, that non-flow, static condition is described as residual pressure. It represents the amount of pressure available in the system when there is no velocity head or friction from moving water. Understanding this helps distinguish it from the pressure that occurs during flow, which drops due to losses as water is drawn from the system. In this context, residual pressure is the term used to describe the non-flow condition, making it the best answer.