Engine companies should not pass their last what when staging?

When staging at the scene of an emergency, engine companies are typically required to have a reliable water source available for firefighting and other rescue operations. Failing to pass their last water source means that they must ensure they are positioned close enough to access this critical resource. Water is essential for effective fire control, and when different companies are responding to an incident, they may need to maintain an adequate supply to support firefighting operations.

Passing the last water source can hinder a company's ability to effectively combat a fire, therefore compromising safety and efficiency at the scene. Hence, having this resource easily accessible is crucial for ensuring that they can respond adequately to the demands of the incident.

The importance of water sources is significant compared to the other options listed, such as communication devices, equipment sources, or rescue teams, which, while important, do not hold the same level of immediate operational necessity in fire suppression scenarios.