On October 1, 2004, about 1440 eastern daylight time, a Rotorway 162F helicopter, N7059F, registered to and operated by a private individual, as a Title 14 CFR part 91 personal flight, lost engine power while in cruise flight in New Smyrna Beach, Florida. Visual meteorological conditions prevailed, and no flight plan was filed. The private-rated helicopter pilot and passenger were not injured, and the helicopter incurred substantial damage. The flight originated at Spruce Creek Airport, Daytona Beach, Florida, the same day, about 1415. The pilot stated that he flew the helicopter southbound along the shoreline, and the first 20 minutes of the flight had been uneventful. Just after performing a right turn to return to his departure airport, he said he noticed that the rotor rpm was at the "low green" portion of the operating range, so he lowered collective and increased throttle input, but the rpm continued to drop to the "mid- yellow" range. He said he initiated an autorotation from about 400 feet AGL, and touched down in a level attitude, with zero forward speed and minimum vertical velocity, into the water. He added that shortly after impacting the water the helicopter rolled 90 degrees to the left, and came to rest in about 3 feet of water. After recovery from the water, the helicopter was examined, and no anomalies were noted. In addition, the engine was removed and shipped to the manufacturer, Rotorway International, Chandler, Arizona, and a detailed examination was performed under the supervision of an FAA inspector. The examination revealed that the engine had accumulated rust consistent with it having been in salt water, however no anomalies were noted. The Fully Automated Digital Electronic Control (FADEC) was examined by the manufacturer, Electronic Concepts & Engineering, Inc., Holland, Ohio, and the damage sustained as a result of the emersion in salt water did not permit recovery of data.