What does residual pressure in a water supply system refer to?

• A. The Pressure When Water Is Not Moving
• B. The Maximum Pump Pressure
• C. The Pressure After The Pump Stops
• D. The Pressure That Remains In The Hose Or Mains While Water Is Flowing

Answer: (D)

When water is moving, the pressure in the system isn’t the same as when it’s still. The pressure that stays in the hose or mains while water is flowing is the residual pressure. This value reflects what the line can actually deliver at the nozzle during active flow, after accounting for friction losses, fittings, and elevation changes along the path. It’s what you monitor to ensure there’s enough pressure at the point of use during a pump operation. It isn’t the maximum pump pressure (that’s the pump setting) and it isn’t the pressure after the pump stops (that would be static pressure with no flow). So the residual pressure is the pressure that remains in the hose or mains while water is flowing.