Narrative:

On may/sat/01, at departure time, received a maintenance call to aircraft. The water was running from the faucets in the forward lavatory and would not shut off. The aircraft was completely loaded and ready to go. I noticed a placard on the mirror and that the handle had been removed from the hot water spigot. The supply shutoff valve would not function so I proceeded to cap off what I thought was the leaking valve. I reinstated water pressure and the leak had stopped. Unfortunately, I did not know the hot water valve was already on MEL for an intermittent leak. The sticker on the logbook just stated 'forward lavatory water inoperative.' satisfied that I had fixed the leak, I called maintenance control and secured an MEL to continue operations. The water from the hot valve must have started leaking again, probably due to a passenger trying to wash up (pressing on the valve even without the handle attached). On the MD80 (that we fly) the forward lavatory sink drains into the forward lavatory tank not overboard. The leak must have continued until the lavatory tank was full, and then spilled over into the aircraft causing damage to the equipment below. The result was expensive repair.

Related reports:

Google
 

Original NASA ASRS Text

Title: AN MD80 WAS DISPATCHED IN NON COMPLIANCE WITH A DEFERRED LAVATORY VALVE LEAKING BUT NOT CAPPED OFF TO PREVENT LEAKING. WATER OVERFLOWED INTO ELECTRONICS COMPARTMENT.

Narrative: ON MAY/SAT/01, AT DEP TIME, RECEIVED A MAINT CALL TO ACFT. THE WATER WAS RUNNING FROM THE FAUCETS IN THE FORWARD LAVATORY AND WOULD NOT SHUT OFF. THE ACFT WAS COMPLETELY LOADED AND READY TO GO. I NOTICED A PLACARD ON THE MIRROR AND THAT THE HANDLE HAD BEEN REMOVED FROM THE HOT WATER SPIGOT. THE SUPPLY SHUTOFF VALVE WOULD NOT FUNCTION SO I PROCEEDED TO CAP OFF WHAT I THOUGHT WAS THE LEAKING VALVE. I REINSTATED WATER PRESSURE AND THE LEAK HAD STOPPED. UNFORTUNATELY, I DID NOT KNOW THE HOT WATER VALVE WAS ALREADY ON MEL FOR AN INTERMITTENT LEAK. THE STICKER ON THE LOGBOOK JUST STATED 'FORWARD LAVATORY WATER INOP.' SATISFIED THAT I HAD FIXED THE LEAK, I CALLED MAINT CTL AND SECURED AN MEL TO CONTINUE OPS. THE WATER FROM THE HOT VALVE MUST HAVE STARTED LEAKING AGAIN, PROBABLY DUE TO A PAX TRYING TO WASH UP (PRESSING ON THE VALVE EVEN WITHOUT THE HANDLE ATTACHED). ON THE MD80 (THAT WE FLY) THE FORWARD LAVATORY SINK DRAINS INTO THE FORWARD LAVATORY TANK NOT OVERBOARD. THE LEAK MUST HAVE CONTINUED UNTIL THE LAVATORY TANK WAS FULL, AND THEN SPILLED OVER INTO THE ACFT CAUSING DAMAGE TO THE EQUIP BELOW. THE RESULT WAS EXPENSIVE REPAIR.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.