PA32 Pilot reported engine roughness resulted in successful return to departure airport. Pilot suspected fuel contamination.

Narrative

Mission: Local IFR for multiple practice approaches at ZZZ. 2 persons aboard; PIC and safety pilot/instructor CFII. Aircraft went through a comprehensive proper pre-flight inspection. Engine start and checklists were completed and were normal. Engine run-up to include magneto checks and prop governor check were satisfactory. All engine instruments were indicating 'Green'; i.e. normal readings. take-off run was normal and all engine instruments/indications were normal. Full-power take-off was normal. At 700 ft. power was adjusted for climb power setting when engine roughness was noticed. There was no reading of the #2 EGT during climb out. Tower switched to Approach control and Approach Control issued a new heading to 240. As the aircraft turned left from 330 to 240 engine roughness increased and continued to increase violently. [Priority handling was requested] and aircraft was cleared to land on Runway XX. Aircraft landed uneventfully on the Runway. Upon exiting the Runway on the next available Taxiway the engine quit. Speculation; water-ice in the fuel tank. Temps were extremely cold. Aircraft was topped off with fuel 8 days prior. The aircraft was stored in a heated hangar. Possible solution; extraordinary care should be taken to drain adequate fuel from the tanks when weather condition are conducive for moisture/water/ice in fuel tanks.