The flow or quantity of water moving through a hose or nozzle is measured by its volume and is usually given in:

The flow or quantity of water moving through a hose or nozzle is commonly measured in gallons per minute (GPM). This unit provides a specific measurement of how much water is being moved each minute, which is particularly useful in firefighting operations for evaluating the effectiveness of a nozzle and the capabilities of various pumping systems. GPM is widely used in the fire service as it allows for a clear understanding of the flow rates necessary to combat fires efficiently.

Other units of measurement like liters, barrels, and cubic feet are less commonly used in the context of firefighting. While liters could be relevant in other fluid measurement contexts, GPM is more standardized in the U.S. fire service, ensuring consistency in operations. Barrels are typically associated with volume measurements in oil and similar liquids, which is not relevant to firefighting. Cubic feet, though a measure of volume, does not provide the time component critical to assessing the flow rate in emergency situations like GPM does.