Narrative:

Because a previous crew had written up the potable water system gauge; the MEL requires that the water be serviced at each departing station. Throughout this flight; we felt 3 unusual 'bumps' with slight vibration and noise each time. The first bump occurred about 10 minutes after leveloff in cruise although at the time I thought it was the flight attendant pushing the service cart into the dock at the same time we hit slight turbulence because the sound was behind the cockpit. We realize now that that was actually the first and mildest of the 3 bumps. The flight attendant called later to say that the water gauge had gone from 60 gallons to 35 gallons and that they had no water throughout the cabin. Because the gauge had been written up; the readings were not unusual; but the lack of water was. About 1 hour 30 minutes later; the second jolt occurred with a sound that we did not recognize. The flight attendant called up and asked if we had heard the noise and felt the vibration which we were trying to troubleshoot at that point. There were no engine indications or annunciator lights indicating a possible compartment door opening. As quickly as the bump was felt; it went away. We continued while still trying to figure out what was going on such as cargo shifting or a loose service panel that was possibly opening; but that we had no indicator light for. Then about 40 minutes prior to landing; approaching the coastline; we got the biggest of the 3 jolts that the passengers actually were concerned about. The flight attendant called and said a passenger seated at 14D had come forward to say that whatever it was felt like it had just happened beneath her seat. After an uneventful descent and landing; the captain and I both did a walkaround with a maintenance person and discovered that ice had formed because the potable water valve was wide open with the service door closed. There was a dent/gash on the inboard side of the right engine along with dents in the leading edges of the right inboard wing and stabilizer. Knowing now what was going on; I will strongly suggest to future captains that we land at the nearest suitable field before any further damage occurs; no matter how brief the bumps may be; with or without indications. Callback conversation with reporter revealed the following information: the reporter advised that a ground crewman discovered a large chunk of ice at the service door. There were holes and gouges in the right engine cowling which they assume were the result of previous chunks breaking away. The impacts and thumping experienced by the passengers and crew were almost certainly the result of the ice striking the aircraft as it traveled aft. He stated there was no obvious aerodynamic buffeting of any sort prior to the reported bumps and thumps.

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Original NASA ASRS Text

Title: B757-200 experienced alarming bumps in flight which were the result of ice forming around the potable water service door due to the servicing valve either malfunctioning or a failure of the ground crew to properly secure it after servicing.

Narrative: Because a previous crew had written up the potable water system gauge; the MEL requires that the water be serviced at each departing station. Throughout this flight; we felt 3 unusual 'bumps' with slight vibration and noise each time. The first bump occurred about 10 minutes after leveloff in cruise although at the time I thought it was the Flight Attendant pushing the service cart into the dock at the same time we hit slight turbulence because the sound was behind the cockpit. We realize now that that was actually the first and mildest of the 3 bumps. The Flight Attendant called later to say that the water gauge had gone from 60 gallons to 35 gallons and that they had no water throughout the cabin. Because the gauge had been written up; the readings were not unusual; but the lack of water was. About 1 hour 30 minutes later; the second jolt occurred with a sound that we did not recognize. The Flight Attendant called up and asked if we had heard the noise and felt the vibration which we were trying to troubleshoot at that point. There were no engine indications or annunciator lights indicating a possible compartment door opening. As quickly as the bump was felt; it went away. We continued while still trying to figure out what was going on such as cargo shifting or a loose service panel that was possibly opening; but that we had no indicator light for. Then about 40 minutes prior to landing; approaching the coastline; we got the biggest of the 3 jolts that the passengers actually were concerned about. The Flight Attendant called and said a passenger seated at 14D had come forward to say that whatever it was felt like it had just happened beneath her seat. After an uneventful descent and landing; the Captain and I both did a walkaround with a maintenance person and discovered that ice had formed because the potable water valve was wide open with the service door closed. There was a dent/gash on the inboard side of the right engine along with dents in the leading edges of the right inboard wing and stabilizer. Knowing now what was going on; I will strongly suggest to future Captains that we land at the nearest suitable field before any further damage occurs; no matter how brief the bumps may be; with or without indications. Callback conversation with Reporter revealed the following information: The reporter advised that a ground crewman discovered a large chunk of ice at the service door. There were holes and gouges in the right engine cowling which they assume were the result of previous chunks breaking away. The impacts and thumping experienced by the passengers and crew were almost certainly the result of the ice striking the aircraft as it traveled aft. He stated there was no obvious aerodynamic buffeting of any sort prior to the reported bumps and thumps.

Data retrieved from NASA's ASRS site as of April 2012 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.