water pumps,Does the water pump need to be replaced if the water pump belt is showing signs of wear? Or just the belt?

My dealership service department has been recommending that I replace my water pump each time I bring my car in for service even though I don't have any issues. Now they are saying the belt is showing signs of cracks and should be replaced along with the water pump. Do both have to be replaced or just the belt?

My car has 12700 miles.
My car has an automatic transmission.