Narrative:

Aircraft service error. We were in cruise on an ocean track approaching an intersection which is just about the area that we lose ACARS communication when the flight attendants reported that they had no water for galleys. We had a potable water servicing slip and the gauge in the forward galley read 'full.' as this is a 5 hour full flight, I was interested in getting water pressure if possible, so finally called maintenance (VHF) to see if they could suggest anything. In our discussion they mentioned that the fill valve handle, if left open, would cause lack of pressure, but that the service door itself would not be closed if that were the case. Knowing we were about to lose communication I asked maintenance to let dispatch know if they had further ideas. A message soon came from dispatch which was incomplete so I had comrdo patch us through and found that maintenance controller was concerned about a leak outside of aircraft and that I might consider returning to ZZZ. I felt this was the most prudent action I could take. We were able to get a clearance through commercial radio for a descent to FL310 and a left turn direct ZZZ. I went ahead and declared an emergency even though we were operating normally. We landed about an hour later with no problems. Even though a mechanic told me they had found the handle partially open the logbook did not reflect that condition. I do not remember the exact signoff. One note -- our flight attendants had not made coffee nor used water for any other reason until we reached altitude, so we had no reason to suspect a problem earlier in the flight. Had preflight procedures included a check for water pressure we might have saved the company the thousands of dollars this incident undoubtedly cost. At any rate the problem was rapidly fixed and after pushback we made sure the right engine was pressurizing the water system and we were again under way.

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Original NASA ASRS Text

Title: B757-200 CREW RETURNED TO THEIR DEP ARPT AFTER THE WATER FILL VALVE WAS NOT IN THE CLOSED POS. THEY DID NOT HAVE POTABLE WATER.

Narrative: ACFT SVC ERROR. WE WERE IN CRUISE ON AN OCEAN TRACK APCHING AN INTXN WHICH IS JUST ABOUT THE AREA THAT WE LOSE ACARS COM WHEN THE FLT ATTENDANTS RPTED THAT THEY HAD NO WATER FOR GALLEYS. WE HAD A POTABLE WATER SVCING SLIP AND THE GAUGE IN THE FORWARD GALLEY READ 'FULL.' AS THIS IS A 5 HR FULL FLT, I WAS INTERESTED IN GETTING WATER PRESSURE IF POSSIBLE, SO FINALLY CALLED MAINT (VHF) TO SEE IF THEY COULD SUGGEST ANYTHING. IN OUR DISCUSSION THEY MENTIONED THAT THE FILL VALVE HANDLE, IF LEFT OPEN, WOULD CAUSE LACK OF PRESSURE, BUT THAT THE SVC DOOR ITSELF WOULD NOT BE CLOSED IF THAT WERE THE CASE. KNOWING WE WERE ABOUT TO LOSE COM I ASKED MAINT TO LET DISPATCH KNOW IF THEY HAD FURTHER IDEAS. A MESSAGE SOON CAME FROM DISPATCH WHICH WAS INCOMPLETE SO I HAD COMRDO PATCH US THROUGH AND FOUND THAT MAINT CTLR WAS CONCERNED ABOUT A LEAK OUTSIDE OF ACFT AND THAT I MIGHT CONSIDER RETURNING TO ZZZ. I FELT THIS WAS THE MOST PRUDENT ACTION I COULD TAKE. WE WERE ABLE TO GET A CLRNC THROUGH COMMERCIAL RADIO FOR A DSCNT TO FL310 AND A L TURN DIRECT ZZZ. I WENT AHEAD AND DECLARED AN EMER EVEN THOUGH WE WERE OPERATING NORMALLY. WE LANDED ABOUT AN HR LATER WITH NO PROBS. EVEN THOUGH A MECH TOLD ME THEY HAD FOUND THE HANDLE PARTIALLY OPEN THE LOGBOOK DID NOT REFLECT THAT CONDITION. I DO NOT REMEMBER THE EXACT SIGNOFF. ONE NOTE -- OUR FLT ATTENDANTS HAD NOT MADE COFFEE NOR USED WATER FOR ANY OTHER REASON UNTIL WE REACHED ALT, SO WE HAD NO REASON TO SUSPECT A PROB EARLIER IN THE FLT. HAD PREFLT PROCS INCLUDED A CHK FOR WATER PRESSURE WE MIGHT HAVE SAVED THE COMPANY THE THOUSANDS OF DOLLARS THIS INCIDENT UNDOUBTEDLY COST. AT ANY RATE THE PROB WAS RAPIDLY FIXED AND AFTER PUSHBACK WE MADE SURE THE R ENG WAS PRESSURIZING THE WATER SYS AND WE WERE AGAIN UNDER WAY.

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.