Welcome to JustAnswer.com! My name is DriveFast71(Ron) and I will do my best to answer all of your questions completely and accurately.
This is actually been a debate and different mechanics will give a different opinion. In MY opinion, I do believe the water pump should be replaced when the timing belt is replaced. I also recommend to my customers that if the tensioner or any of the idler pullies show any sign of wear, they should be replaced as well. Considering the amount of labor that it takes to get to the belt (which runs the water pump) I think it's worth a few extra dollars in parts to get it done, and have the good feeling that everything is new and wearing in at the same time. If the water pumps goes bad (or a pulley or tensioner) after the belt is replaced, you pay for the labor all over, and in some cases, a new belt due to water damage.