On May 18, 2018, about 2032 central daylight time, an experimental Vans RV7A airplane, N667AZ, was substantially damaged when it was involved in an accident near Hanover Park, Illinois. The airline transport pilot sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that he completed a normal preflight inspection that revealed no anomalies with the airplane or its engine. The pilot noted that both wing fuel tanks were completely full before the flight, and he did not observe any contamination in the fuel samples that he obtained from each wing tank during his preflight. The airplane was not equipped with a drainable fuel filter assembly. The pilot reported that the engine started without hesitation and that there were no anomalies during the before-takeoff engine runup. The pilot performed a normal takeoff from runway 11 and entered a left downwind to depart from the airport traffic pattern. As the airplane climbed through 1,600 ft mean sea level, the engine began to run rough and one of the cylinders had an elevated exhaust gas temperature. The pilot stated that he turned on the fuel boost pump, switched fuel tanks, and ensured that the throttle, mixture, and propeller controls were full forward. The engine operation did not improve despite the pilot's corrective actions and the airplane was unable to maintain altitude. The pilot initially began a turn back toward the airport, but decided to maneuver toward a nearby vacant field to remain clear of a densely populated area. The pilot stated that the airplane nosed over upon touchdown on the soft field, and the pilot was able to exit the airplane with minor injuries. A postaccident examination of the airplane and its engine was completed by a National Transportation Safety Board investigator and a Federal Aviation Administration airworthiness inspector. The fuselage, both wings, and the empennage were substantially damaged during the accident. The airplane was equipped with only two fuel sumps, one located under each wing; the fuel filter did not have a sump. Fuel samples taken from each wing tank sump were free of water contamination. A sample collected from the fuel supply line connected to the fuel injector servo inlet contained a mixture of 100 low-lead aviation fuel and a small amount of water. The electric fuel pump was used to obtain an additional fuel sample, which also contained water. The fuel filter was removed from the fuselage and its contents drained; water detection paste revealed the presence of water. Water was also detected in the filter screen. Examination did not reveal any mechanical anomalies that would have precluded normal engine operation during the flight. A review of maintenance documentation revealed that, on February 20, 2017, water and particulate contamination were observed in the fuel filter and the fuel injection servo finger screen during a routine condition inspection. The final airframe logbook entry, dated March 27, 2018, did not indicate if any water or particulate contamination was observed during a routine condition inspection; however, the logbook entry did note that the fuel filter and fuel injector servo finger screen were removed and cleaned. At the time of the accident, the airplane had flown 4.6 hours since the last condition inspection.