The pilot departed in a Piper PA-28-181 with full tanks. After flying for 2.2 hours, the engine lost power and the pilot ditched the airplane in the Hudson River. When interviewed he reported that he had not switched tanks. The FAA reported that after the airplane was recovered from the river, the right tank was full of fuel, and the left tank had about 5 gallons of water, and less than half a cup of fuel. The fuel selector was found set to the left tank.