Water curtain system is one of the active fire suppression system (Active fire suppression system means it becomes active only when there is fire). As the name itself defines, if forms a curtain to prevent spread of smoke / heat / flame from fire captured area to no fire area.
In the aspect of fire & life safety, compartmentation of building plays an important role. Compartmentation means providing barrier in a large area so that fire / heat / smoke cannot propagate. The barrier can be fire rated wall (or any assembly) or fire curtains or water curtain. Since the question is about water curtain system, I will explain what is it and how does it work.
Water Curtain Pump is connected to the water curtain nozzle through deluge valve. From pump to deluge valve, the pipelines are normally flooded (flooded here means the pipe line contains water pressurized). From deluge valve to water curtain nozzle, the pipelines are dry (no water)