As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
VISIBLE SMOKE UNDER AFT LEFT LAV SINK IN FLIGHT. WATER HEATER WAS TURNED OFF. CONDITION DID NOT GET WORSE. DEBRIEF CREW IDENTIFIED SOURCE OF SMOKE TO BE WATER HEATER UNDER SINK. PERFORMED TSM 24-00-00-810-823-A. PLACED WATER HEATER ON MEL 38-10-01B. MAINTENANCE ACTION COMPLIED WITH. OK TO CONTINUE .