On August 3, 1996, about 1040 Atlantic standard time, a privately owned homebuilt Challenger II Special, N113JM, crashed during an attempted forced landing after takeoff from a private grass strip near Toa Baja, Puerto Rico. 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 pilot, the sole occupant, sustained serious injuries. The flight was originating at the time of the accident. The pilot stated that he performed a preflight of the airplane before takeoff and observed no water in the fuel system. He also performed an engine run-up before takeoff with no discrepancies noted. After takeoff about 200 feet above ground level, the engine rpm dropped uncommanded from 6,300 to 2,000 and he was unable to maintain altitude. He initiated a descent for a forced landing and with obstructions ahead, he maneuvered to avoid the obstructions. The airplane then stalled and impacted the ground. His injuries consisted only of a fractured T12 vertebra. Examination of the airplane by an FAA Airworthiness Inspector revealed water contamination in the fuel filter located in the engine compartment area, in a fuel line to the carburetor, and in the carburetor bowls. Also discovered was a separation of the front seat throttle control swivel from the throttle control arm. The airplane fuel tank does not have a drain installed.