In the scene where the building is burning all over and the firemen are spraying water, for one second the scene shows the driver standing at the pump panel of the fire truck. The gauges on the pump panel are all on zero. They switch back to the firemen on the end of the hose lines and water is coming out of the hose. The scene switches back to the driver standing at the pump panel and the gauges are still on zero. If there were no pressure on the hose, no water would come out of the nozzle.