On September 20, 1996 about 1230 eastern daylight time, N2738K, a Cessna 180K airplane, had a loss of engine power during initial takeoff climb, and was forced landed into trees at Derry, New Hampshire. Visual meteorological conditions existed. The certificated private pilot, the sole occupant, was not injured. The airplane was substantially damaged. The destination was Auburn, Maine. The flight was operated under 14 CFR Part 91. The pilot reported that the "...aircraft was tied out for 3 weeks ..." prior to the accident flight. He stated that the preflight was done to include "...draining sumps." The pilot reported that he performed an engine run-up of about 5 minutes duration, taxied for departure and took off. He stated that at approximately "...200 [feet] power lost - crashed in trees at end of field - water in fuel." A post accident examination of the aircraft was performed by a Federal Aviation Administration Airworthiness Inspector. The Inspector reported, "Removed main fuel line from fuel strainer to carburetor and found it full of water. Also discovered two fuel leaks on the top of the right wing. The pilot/owner Mr. Edwin Simonsen said he had noticed this seeping before the accident. The aircraft had been parked for a few weeks before this accident. This area had experienced heavy rain recently." "When Mr. Simonsen performed his preflight the tail of the aircraft was up at least a foot or more than normal because he tied it down with the nose on a downward slope. Subsequently, when he sumped the tanks and fuel strainer he found only fuel. The water had settled to the forward section of the tanks.