Wet-pipe sprinkler systems are the most common fire suppression systems.  In a wet-pipe system, either the water supplied by the municipality or the water supplied from a fire pumping station provides constant pressure for the system.  When a sprinkler in this system is activated through melting of its fusible link, water is immediately discharged onto the fire.  Water will flow until the fire is extinguished and until the fire marshal shuts off the water supply.