The 30,000-hour commercial pilot reported that the turbine-powered agricultural airplane made a hard landing after experiencing a loss of engine power. The pilot added that he was performing the last aerial application flight of the day when the engine lost power. The pilot further stated that the tailwheel equipped airplane had been refueled from a 1,000 gallon fuel tank located at his property. He added that the fuel storage tank was contaminated with water due to the torrential rain experienced this season. The rain water entered the fuel storage tank through a worn-out seal on the tank's refueling port. The airplane came to rest on a rough and uneven clearing located about 3 miles from the point of departure. The landing gear separated from the aircraft upon landing and the fuselage sustained structural damage to the underside of the aircraft. The pilot was not injured during the mishap. A post accident examination of the airplane conducted by a Federal Aviation Administration inspector revealed that water contamination was present in the aircraft's engine fuel filter.