Date: 201703
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Parked
Aircraft component: Drinkable/Waste Water Syst
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Second reporter function: Captain; Pilot Flying
Anomaly: Aircraft Equipment Problem Less Severe; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Person Flight Attendant
When detected: Aircraft In Service At Gate
Result: General Evacuated; General Maintenance Action
Contributing factors: Aircraft; Procedure
Primary problem: Aircraft

Narrative: After completing the parking checklist the aft flight attendant noticed a smell of smoke coming from the aft portion of the cabin. After checking it out the captain asked me to contact ground control to get the fire trucks rolling to the aircraft. He also asked me to contact operations to get maintenance out to the aircraft. After accomplishing those two things I stayed at the front of the aircraft and kept the cleaning crew and catering from entering the aircraft. After the fire department declared all clear we handed the aircraft over to maintenance.


Second narrative: We had a normal flight up until just after finishing parking checklist. As we were packing our bags; the aft FA called saying there was a smoke smell in aft cabin. We had just put on ground power and shutdown APU which will matter later in description. I talked with the FA to determine source of smell. We thought that maybe it was coming from brakes since aft cabin door was open; or air conditioning system and it would dissipate soon since APU had just been shut down. We could not see or smell any indication of smoke in first 3/4 of aircraft so I called operations and I directed my FO to call ground to send fire personnel to our aircraft.I then started working my way to aft of aircraft since the aft FA had already started announcing over PA for remaining passengers to leave everything and exit aircraft immediately. A mechanic showed up at that point and we continued to rear of plane but could not smell or see any smoke. Once we reached around 5 rows from rear of plane I could smell smoke and as we went further we could see the smoke. Fire personnel soon showed up and we were trying to determine source of smoke which was dissipating.The plane was empty of passengers at that point so mechanic put the APU back on as we tried to find source. That completely cleared smell. The smell was strongest 3 rows from rear when it happened according to the FA. I remembered that prior to departure there was no water pressure in entire aircraft. Maintenance repaired issue and signed off write up and we received new release. Apparently the only system that is below the 3rd row toward rear of cabin is the water system compressor which only works when there is no pneumatic air pressure from APU or engines. Once we switched to ground power and shutdown APU; the water compressor started and apparently began to smoke. It stopped again when Maintenance turned APU back on as we tried to investigate source of smoke. All in all a little confusing but we worked together as a team and everyone was safe.


Synopsis: B737 flight crew was informed by a Flight Attendant that there was smoke in the aft cabin after gate arrival. The problem was traced to a faulty potable water system compressor.