The pilot stated that he was conducting a demonstration flight with a passenger onboard in the amphibious experimental amateur-built airplane. He reported that after takeoff, while explaining the operational characteristics of the airplane to his passenger, he forgot to raise the airplane's landing gear as was his custom. Later in the flight, while performing a low-altitude slow flight maneuver over water, the landing gear made contact with the water's surface. The airplane subsequently nosed over into the water and came to rest upright, resulting in substantial damage to the windscreen and front deck. The pilot reported no pre-impact mechanical malfunctions or failures that could have precluded normal operation of the airplane.