On April 20, 1999, at 1834 hours Pacific daylight time, a Cessna R182, N7317X, was substantially damaged when the right wing collided with a sign during an off-airport emergency landing following loss of engine power near San Luis Obispo, California. The commercial pilot was not injured. Visual meteorological conditions prevailed and no flight plan was filed. The personal flight, operated by the owner under 14 CFR Part 91, departed from San Luis Obispo at 1800. The pilot reported that he was returning for landing when the engine stopped abruptly about 6 miles northwest of the airport. The aircraft descended through a stratus cloud layer and broke out beneath a 900-foot ceiling. The pilot determined that the aircraft would not glide to the airport and made an emergency landing in an open field alongside a highway. In his report to the Safety Board, the pilot reported there were no mechanical malfunctions with the aircraft, and that water was found in the carburetor at the emergency landing site. He reported that he drained both fuel tank sumps (left and right), as well as the firewall gascolator as part of his preflight inspection. Inspectors from the San Jose Flight Standards District Office reported that the engine fuel sump contained a clear fluid resembling water, and that the right-hand fuel tank sump drain had a threaded plug installed which precluded routine sampling of the tank for water.