On September 10, 2003, about 1407 eastern daylight time, a float-equipped Piper J5A, N33063, registered to a private individual, landed hard at Jack Browns Seaplane Base, Winter Haven, Florida. Visual meteorological conditions prevailed at the time and no flight plan was filed for the 14 CFR Part 91 personal flight. The airplane was substantially damaged and the private-rated pilot, the sole occupant, was not injured. The flight originated about 7 minutes earlier from Jack Browns Seaplane Base. Before the flight departed, the pilot cleaned the airplane and checked the oil capacity (the engine had 7 quarts of oil). The pilot reported that he checked the fuel in the right wing fuel tank for contaminants, then after noticing the tank was 1/2 full, 5 gallons of 100 low lead fuel were added to the tank. He did not report checking the fuel tank for contaminants after fueling. He performed a preflight to the airplane but later advised the FAA inspector-in-charge (FAA-IIC) that he did not know the airplane had a gascolator installed, and as such, did not check it during the preflight. He started the engine by hand propping it, and after starting, ran the engine for 5 or 6 minutes before securing it due to no indication on the amp meter. The discrepancy was traced to the alternator and it was suggested that the pilot fly the airplane for 1 hour to see if the alternator started working as the airplane had been sitting for 4 months. The pilot was also advised to do some idle taxiing and step taxiing to get the feel for the airplane he had just purchased. The airplane was pushed into the water, the engine was started, and the pilot idle taxied the airplane 5-10 minutes, then did 2 step taxis up and down the lake. He applied power to 1,800 rpm and checked the magnetos and carburetor heat; no discrepancies were reported. He verified the carburetor heat was off, and proceeded to takeoff. At 200-300 feet before reaching the end of the lake, the engine quit. He was unable to attempt a restart due to not having electrical power available, but pumped the throttle in an attempt to restore engine power; the results were unsuccessful. With insufficient lake available to land ahead, he initiated a 180-degree turn, and after completing the turn, flared when the airplane was 10 feet above the water. He reported, "I think I stalled the aircraft at about 20 feet with a slight right wing down." The airplane impacted the water right wing low, which damaged the wing. The airplane was towed to the public jetty, then removed from the water and transported to a nearby facility for further examination. He further reported there was no mechanical failure or malfunction, and he noted a low point in the fuel system beneath the floor boards which prevented water from reaching the gascolator. Several witnesses reported hearing either a sputtering engine or rough running engine after the airplane became airborne; both reported the engine then quit. One of the witnesses who is a pilot reported that after the engine quit, the pilot turned from the northwest to the south, and the pilot began "roundout to level off unusually high (approx 40 feet above water surface. The aircraft stalled [approximately 10 feet off the water resulting in right wing drop." Postaccident examination of the recovered airplane by an FAA airworthiness inspector revealed the gascolator was approximately 1/2 full of water; the carburetor bowl was not examined. The engine was removed from the airplane, placed on a test stand, and found to operate normally. According to the president of the facility that fueled the airplane last, no contaminants were noted in post accident fuel samples taken from the fuel nozzle under pressure, or fuel filter. A check of the fuel supply tank using water finding paste was also negative.