After Draining Both Wing Fuel Tanks, A Significant Amount Of Water Was Observed In The Right Wing Fuel Tank Analysis: The pilot, who was also the owner of the experimental amateur-built airplane’s kit manufacturer, was performing a demonstration flight for potential buyers. The pilot reported that after fueling the airplane, a preflight inspection was performed and no anomalies were found; however, he stated that he did not sump the fuel tanks or the low-point drains. The pilot stated that after performing the engine runup and allowing the engine to reach operating temperatures, he performed a normal take off. At around 300 ft above ground level, the pilot reported that the engine began to “cut out,” and the pilot pulled the throttle bringing the engine to idle.