Engine Timing: Should I replace the water pump with my timing belt?

On a large proportion of engines that have a timing belt (AKA cam belt) the water pump is not only driven by the belt, it forms an important bearing to keep it tensioned correctly.

There are two reasons for having it replaced at the same time.

Firstly, should the water pump fail for any reason, then the timing belt would have to be replaced again as you cannot re-fit a timing belt under any circumstances.

Secondly, should the bearing in the pump fail, the timing belt circuit would be compromised and that could easily end in a catastrophic and expensive timing failure.