Final answer:
The preferred communication method between a water skier and the observer is the use of hand signals, which include common gestures for essential commands.
Step-by-step explanation:
The preferred form of communication between a water skier and the observer is hand signals. These signals are crucial for the safety and coordination between the skier, the driver of the boat, and the observer. Common hand signals include thumbs up for speeding up, thumbs down for slowing down, slashing the neck for stopping, and patting the top of the head to indicate a desire to return to the dock. It is essential for the skier and observer to have a clear understanding of these signals before starting, as vocal commands can be difficult to hear over the noise of the boat and water.