What does the term "residual pressure" refer to in firefighting?

The term "residual pressure" in firefighting refers to the final pressure that exists in a system once water has begun flowing. This pressure is crucial for ensuring that adequate water supply and force are available at the nozzle for effective firefighting operations. When water begins to flow through the system, the dynamics change, and the pressure readings can reflect the available pressure in the system after accounting for losses due to friction and other obstacles in the hoses or apparatus. Understanding this concept is essential for fire apparatus operators, as it directly impacts their ability to deliver water efficiently and effectively during firefighting efforts.