The alternator/water pump belt problems

What is your question?

It is wearing out. Have replaced twice in the last 12 months. It is a ribbed belt. But the water pump pulley is flat. This pulley doesn't run on the back of the belt. This I think is the problem. But this might be the correct set up for the belt. Also have checked all pulleys if running true. All ok. Has anyone come across problems similar???