Your timing belt should be replaced every 60,000 to 90,000 miles and of course that depends on your specific engine. Your water pump is driven by the timing belt, so it has the same amount of wear and hours as your timing belt. It's in your best interest to replace it at the same time to prevent a breakdown or a costly repair. Plus as Jason always puts it "it's cheap insurance."
Give us a call and let us take care of you.