What was found
DURING DESCENT, THE FLIGHT ATTENDANT REPORTED VIA INTERPHONE TO COCKPIT, THAT THE RIGHT AFT LAVATORY SMOKE DETECTOR WAS SOUNDING AND A SMELL OF SMOKE. THE FLIGHT ENGINEER WAS DISPATCHED TO INVESTIGATE. THE FLIGHT ATTENDANT DISCHARGED A PORTABLE FIRE EXTINGUISHER UNDER THE SINK AND TOILET AREA, WHILE THE FLIGHT ENGINEER REMOVED ELECTRICAL POWER BY OPENING THE CIRCUIT BREAKERS OF THE LAVATORY. THE FLIGHT ENGINEER REPORTED SMOKE WAS DIMINISHING AND A UNEVENTFUL LANDING WAS MADE. MAINTENANCE IDENTIFIED THE SOURCE OF SMOKE TO BE FROM THE LAVATORY WATER HEATER. MAINTENANCE REPLACED THE DEFECTIVE WATER HEATER AND NO FUTHER DISCREPANCES WERE NOTED.