The pilot reported that while maneuvering low over the harbor for an aerial application flight he directed his attention inside of the helicopter to program the global positioning system (GPS). Subsequently, the helicopter impacted the water in a level upright position. Despite the pilot's control inputs the engine lost power and the helicopter slowly started to settle and roll onto its left side. The helicopter's main rotor blades, tail rotor blades, and the main rotor head assembly were damaged. The pilot reported no mechanical failures or malfunctions with the helicopter's flight control system or engine prior to the accident.