What is the pressure measured at a residual hydrant when flow readings are taken known as?

When assessing water supply systems, particularly during flow testing of hydrants, the term "residual pressure" specifically refers to the pressure that remains in the system when water is flowing. This measurement is crucial for understanding the available water flow during firefighting scenarios, as it indicates how much usable pressure is left after accounting for the pressure drop caused by the flow.

Residual pressure is different from static pressure, which is the pressure in the system when no flow is occurring. While both measurements are important for evaluating fire hydrant performance, residual pressure specifically tells fire service personnel how effectively they can utilize the hydrant during active operations. By knowing the residual pressure, firefighters can make informed decisions about tactics, equipment, and hose lengths needed to manage a fire effectively.

Understanding the distinction between these types of pressures can aid in maximizing the effectiveness of firefighting resources and ensuring adequate water supply entailed by the flow from the hydrant. This is why the correct answer in this context is residual pressure.