How do you determine when to switch to a secondary water source?

• A. When primary source capacity is sufficient to sustain flows.
• B. When primary source capacity is insufficient to sustain flows required for the operation.
• C. After a fixed time of 15 minutes.
• D. Only when the incident is downgraded.

Answer: (B)

You switch to a secondary water source when the primary source cannot sustain the required flow for the operation. The firefighting pump team must deliver a specific volume at the nozzle to overcome friction losses, elevation, and any other demands on the line. If the primary supply can’t maintain that sustained flow, switching to a secondary source—such as another hydrant, a relay pump, or a drafted source—keeps water moving at the necessary pressure and volume. This choice prioritizes maintaining effective fire attack over rote timing or incident status, and it isn’t based on a fixed time or on downgrading the incident.