USAF Mobile Water Supply (MWS) Fire Practice Test

The important idea here is that hose size directly influences how much water you can push at the required rate. A 2-inch pump line is chosen because, in the MWS setup, it must reliably deliver about 500 gallons per minute while the source tank is filled to about 80 percent. The diameter sets friction losses; with a 2-inch line, the system can maintain that 500 GPM without the pressure dropping too far as the water level changes, which keeps the flow steady when the tank isn’t full. If the line were smaller, friction would limit the flow and you wouldn’t reach 500 GPM; if it were larger, you’d be carrying more weight than needed without gaining practical benefit. The other options aren’t about meeting the specific flow requirement or the headroom needed to sustain it, so they don’t fit as the primary reason for choosing this diameter.