At about 13:00 eastern time, a Cessna 150 was damaged during an emergency landing in a field near Bridgewater. Neither occupant was injured. The pilot designated the PIC said the pilot-rated passenger was a mechanic who had completed an annual inspection on the airplane. The mechanic wanted to take the airplane for a test flight, but did not have a current medical certificate, so he asked the PIC to accompany him on the flight. Prior to the annual inspection, the airplane had not flown for approximately three years. The mechanic checked the main fuel strainer during the annual inspection and did not observe any debris or contamination. About 2 weeks before the accident flight, the mechanic completely filled the tanks with fuel. After the fueling, the engine would not start. The mechanic drained all the fuel and refueled the tanks to capacity, but he did not recheck the main fuel strainer. The PIC sumped the fuel tanks before the accident flight, found water, and continued sumping until the sample was clear. The inspector observed fuel contamination in the main fuel strainer and carburetor.