Which pressure must be measured to calculate the quantity of water flowing through a hydrant discharge?

To calculate the quantity of water flowing through a hydrant discharge, the residual pressure must be measured. Residual pressure is the pressure that remains in the system when water is flowing and is crucial for determining how much water can be delivered under those flow conditions. By measuring this pressure at the discharge side of the hydrant while water is flowing, firefighters can assess the effectiveness of the hydrant, understand the available flow, and make informed decisions about firefighting strategies.

This pressure measurement is essential for ensuring that there is sufficient water supply for firefighting operations. The quality of the water supply can significantly impact the success of firefighting efforts, as insufficient flow can lead to ineffective suppression of fires. When determining flow, it is standard practice to take a residual pressure reading to evaluate the system's capability to provide the necessary fire flow.