The water pump isn't the
problem, it's the propeller. And this doesn't have a replacement time or mileage as it's supposed to last for the life of the car, it's not a service item. But unfortunately the standard propeller is plastic and can break on some cars, causing the car to over-heat. There is a brass version of it from the Audi TT that can be fitted that cures this
problem, but to fit it involves taking off the cambelt, which is why it's recommended that when you get one done, you do the other at the same time