How long before you need to change the Water pump and/or impeller?

I have an '03 250 EFI OX66 (bought new in 2006) I am not having any problems with overheating or with the pressure.....I just heard you should change them every 3 years....Any comments or suggestions? Also where is the cheapest place to get one?

I change mine on the third year

Agree with every 3 years. It is a pain to do, but within the grasp of the average backyard mechanic. I had one let go after 2 years, and sometimes they look good after 3 years, but you don't want to deal with it when you've got a trip or tournament planned!