What is residual pressure in a water distribution system?

Residual pressure in a water distribution system refers to the amount of pressure that remains in the system when water is flowing. This measurement is crucial, especially during firefighting operations, as it indicates the available pressure to support water delivery at a fire scene. When water flows through pipes, friction losses and other factors can reduce the pressure available at hydrants or nozzle outlets. Understanding the residual pressure helps firefighters assess the effectiveness of the water supply being delivered to a firefighting hose line or sprinkler system during the operation.

In fire protection, knowing the residual pressure is important for ensuring there is adequate water supply to combat a fire, as it typically reflects the system's capacity to deliver water under operational conditions. It is distinct from static pressure, which is the pressure in the system when there is no flow occurring. Other choices, such as the maximum pressure a hydrant can deliver or pressure exerted by stored water, do not accurately convey the concept of residual pressure related to the system under flow conditions.