The quantity or flow of water moving through a pipe, hose, or nozzle is measured by:

The quantity or flow of water moving through a pipe, hose, or nozzle refers to the total amount of water being transported within a given time period. This is best described by volume, which quantifies how much fluid is passing through a given point over time, typically measured in gallons per minute (GPM) or liters per second (LPS). Volume essentially conveys the measure of liquid flow, allowing for effective calculations regarding delivery rates, which are crucial for firefighting and other fluid management scenarios.

While pressure relates to the force exerted by the fluid, and velocity signifies how fast the fluid is moving, they do not directly describe the quantity of fluid flow. Capacity typically refers to the maximum amount a container can hold or convey rather than a measurement of flow itself. Thus, the best choice for expressing the amount of water moving through a system is volume.