The pilot reported that he was engaged in moving cattle on a flooded property. On board the helicopter with the pilot was the property owner. While hovering at about 30-40 feet behind some cattle, the pilot's attention was diverted momentarily allowing the engine and main rotor RPM to decay. He was unable to regain rotor RPM and elected to attempt a landing onto a nearby dry patch of ground. In turning the helicopter towards the dry ground, the pilot inadvertently turned down wind, overpitching the main rotor blades. During the ensuing deep flare to land, the tail rotor contacted the water and the main rotor blades severed the tail boom. The helicopter then settled into the water and rolled over. Both the pilot and passenger were able to exit the helicopter safely.