The water supply to the boiler is not "making up the level". as a boiler makes steam and it goes out of the steam drum into the pipes that deliver it to the steam users, the level of water in the steam drum is depleted. some sort of pump is required to replenish the water removed as steam. if the level in the steam drum is decreasing then the pump isnt making up level and this very dangerous. if level cannot be restored before the drum is at some predetermined low-low critical level, all fire should be imediately removed, no exceptions!