After refuelling, the pilot found one of the tanks contaminated with water. The fuel was drained from the tank and clean fuel added. No contamination was found in the subsequent check of the fuel in the tank. The aircraft was then washed using a high pressure water hose. During the following flight, the engines began to run roughly and the pilot decided to carry out a landing in a paddock. The surface of the paddock was rough and the aircraft bounced heavily and groundlooped, collapsing the right gear. The investigation revealed that water had been present in the fuel system for sometime. Because of the design of the fuel system it is not possible to drain the lowest point of the fuel tank while the aircraft is parked. It is probable that the engine rough running was caused by a combination of contaminated fuel and a sticking valve.
