A B777 RAN OUT OF POTABLE WATER INFLIGHT BECAUSE THE WATER TANK FILL VALVE FAILED TO OPEN COMPLETELY DURING FILLING; WHICH IN TURN CAUSED THE OVERFLOWN VALVE TO OPEN. THE GND SVC PERSONNEL; NOTING THE OVERFLOW; BELIEVED THE WATER TANK TO BE FULL.

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OBTAINED WATER SERVICE FORM FOR FLT SHOWING POTABLE WATER SERVICED TO FULL. AT A POINT MORE THAN TWO HOURS FROM DEST POTABLE WATER EMPTY. FOURTEEN CREW AND 247 PAX. MY POST FLT RESEARCH REVEALED THAT THIS ACFT HAD EXPERIENCED THE SAME PROB 4 TIMES WITHIN THE PREVIOUS TWO WEEKS. THE B777 FLEET HAS HAD A HISTORY OF WATER FILL VALVE PROBS; SPECIFICALLY THE FILL VALVE DOES NOT OPEN TO THE FULL POSITION WHEN SELECTED BY WATER SERVICE PERSONNEL. WATER STARTS COMING OUT OF THE OVERFLOW BEFORE THE TANK IS FULL. THE SERVICE PERSONNEL WRONGLY ASSUME THE TANK IS FULL; STOP THE WATER INFLOW AND REPORT THE TANK FULL. THE B777; AND I AM TOLD THE B737; WATER TANK QUANTITY INDICATIONS HAVE BEEN DE-ACTIVATED IN YET ANOTHER ILL ADVISED COST SAVING EFFORT. HAVING NO WATER ON BOARD IS A SAFETY PROB. THE LAVS ARE USED MOST DURING THE LAST TWO HOURS OF FLT. NO WATER MEANS NO WAY TO FLUSH LAVS AND NO WAY TO WASH AFTER USING THE LAV. NO WATER TO DRINK; NO COFFEE OR TEA; EITHER. IRATE PAX CAN QUICKLY TURN INTO UNCOOPERATIVE OR EVEN HOSTILE PAX. A VERY REAL CONCERN WOULD BE A LAND NOW EMER SUCH AS AN ENG FIRE REQUIRING A DIVERSION INTO A FIELD WITH LITTLE OR NO PERSONNEL ON THE GND TO ASSIST. RUSSIA AND OTHER PLACES HAVE CONCRETE BUT NO GND HELP. AN ACFT COULD BE ON THE GND FOR SEVERAL DAYS WAITING RESCUE. HAVING NO WATER COULD QUICKLY MAKE THE SITUATION UNSURVIVABLE. REACTIVATE THE WATER QUANTITY INDICATION SYSTEMS. I KNOW THIS IS NOT THE WAY THE ACR OR THE FAA ATTACHED TO THE AIRLINE WORKS -- BUT WOULD IT NOT BE PRUDENT TO FIX A KNOWN PROB BEFORE DISASTER STRIKES?