The pilot reported that he did not sump the fuel tanks during the airplane's preflight inspection, thinking that because the outside temperature had remained below freezing, any water would have been in the form of ice. Shortly after takeoff, about 100 feet, the engine lost power, and the airplane struck trees about 1/4 mile from the end of the runway. The pilot further stated that he thought the cause of the accident was water in the fuel, and that draining the sumps would have prevented the power loss. Post-accident examination of the airplane revealed water in the gascolator.