AN AIRBUS 320 WAS DISPATCHED IN NON COMPLIANCE WITH A REAR GALLEY WATER LEAK DEFERRED; BUT WATER TO AFT GALLEY NOT SHUT OFF. REAR GALLEY FLOODED.

Narrative

REAR GALLEY DEFERRED DUE TO SOME PROB. WATER VALVE WAS STILL OPEN AND WHILE ENRTE AT FL350 FLOODED REAR GALLEY TO THE EXTREME. STANDING WATER IN GALLEY AND UP TO 2 ROWS IN REAR OF ACFT. MAINT FAILED TO CLOSE THE SHUTOFF VALVE PRIOR TO FLT (ACFT CAME IN FROM ZZZ1). THE FLT ATTENDANTS COULD NOT FIND THE SHUTOFF VALVE TO STOP THE WATER. WATER CONTINUED TO FLOW UNTIL OUR JUMP SEATER; AIRBUS CAPT; RETURNED TO THE REAR AND SHUT THE FLUID FLOW OFF. MAJOR MISTAKE BY MAINT FOLLOWED BY LACK OF TRAINING OR POOR PERFORMANCE BY THE FLT SVC TO SHUT THE WATER OFF. THIS COULD HAVE BEEN VERY DANGEROUS. I FEEL THIS WAS A MAJOR BREACH OF THE SAFETY NET OF OUR OP. DO NOT KNOW ALL THE POTENTIAL DAMAGE WHICH COULD RESULT. I DO KNOW ACFT ARE NOT SWIMMING POOLS. THE WATER COULD HAVE CREATED CTL PROBS; ELECTRICAL SHORTS FOR PAX AND CREW IN GALLEY; AS WELL AS MAJOR ELECTRICAL PROBS. THIS WAS A POTENTIAL PROB WHICH COULD HAVE RESULTED IN A HULL LOSS. VERY UPSET THAT MAINT DID NOT SHUT THE VALVE OFF AND EQUALLY UPSET FLT SVC COULD NOT FIND THE VALVE SHUTOFF. SUGGEST CREW OPTION BE GIVEN TO FIX SUCH PROBS IN THE FUTURE. NOW; AS I UNDERSTAND IT; WE ARE NOT TO LEAVE THE COCKPIT. PLEASE ADVISE AS TO THE BEST OPTION IN ADVENT THAT NO COCKPIT CREW MEMBER IS AVAILABLE FOR MAINT INTERVENTION.