To prevent the vehicle from hydroplaning, it is essential to **reduce speed**. This is because **aquaplaning** occurs when the tires cannot displace all the water from the road, causing the vehicle to lose traction and skid. This phenomenon is more likely at **high speeds** and with worn or very wide tires. Therefore, by reducing speed, the risk of aquaplaning is decreased, as the tires have more time to expel the water and maintain contact with the road.

Additionally, driving in the rain presents additional challenges, such as **reduced visibility** and less tire grip, which increases the braking distance. Therefore, it is crucial to **reduce speed** to have more control over the vehicle and be able to react appropriately to any unforeseen events. It is also recommended to keep the tires in good condition and brake gently to prevent the wheels from skidding.

In summary, reducing speed is the most effective measure to prevent aquaplaning and ensure safe driving in rainy conditions.