Instructions
Start the game and select a plane. Takeoff and get your plane into the air. Switch the camera view to "External" so you have a better view of your surroundings.
Press the "G" button to retract the landing gear while your plane is in the air. It is impossible to land on water while the landing gear is out.
Turn your plane toward a body of water and start your descent. Line your plane up with the water and cut your airspeed. Press "F3" to decrease the throttle on your plane and keep your speed below 300 knots.
Press "2" on the numeric keypad or pull back on your flight stick to bring the pitch of the nose up. The aim is to hit the water with the nose of the plane angled upward. As long as the tail section of the plane hits the water first and you keep the nose pointed upward during the landing, the plane will float until it comes to a standstill.