During cruise, the engine lost partial power. The pilot stated he applied carburetor heat, and shortly thereafter, the engine lost all power. During an emergency landing on mountainous wooded terrain, the airplane 'clipped' trees and impacted the ground, then it slid about 30 ft and came to rest inverted. An exam of the airplane revealed no airframe anomalies. The engine was inspected and water was found in the gascolator, carburetor float bowl and accelerator pump housing; source of the water contamination was not determined. Mice were found in the carburetor air box and venturi area. One mouse was lodged in the throttle valve. Receipts showed the airplane received about 17 gallons of fuel on the day before the accident. Since then, the airplane had flown about 1 hr. The pilot said that before each flight, he drained each fuel drain. He said water was found in the fuel samples, but he continued to drain the fuel until no more water was detected.