The pilot made an aerial inspection of development of part of the Mission property. On returning to the strip he positioned the aircraft on base leg at 500 feet, but before he turned left to make the final approach to land he noticed new developmental work and turned right toward it to make a closer inspection. As the aircraft turned towards the area and toward rising ground covered with tall trees, a water bottle alongside the pilot's seat fell over and rolled towards the rear of the aircraft spilling the contents. The pilot held the control column with his left hand, turned in his seat and made several attempts to right the bottle before he succeeded. During these attempts the aircraft descended to tree top height over the higher terrain. The pilot looked up at the same time as he felt the aircraft striking the trees. He levelled the aircraft, pulled up and applied power and made a landing without further incident at the Mission airstrip. Inspection disclosed extensive damage to the flaps and leading edge of the wings, that portion of the tailplane was missing and that the starboard elevator was supported by one hinge.