My best advice is that you replace it when it starts to look like this!
I'm not sure how old this tank was, but the bottom has been rusty for a long time. Other than the rust, there were no obvious signs that something was wrong until water started leaking everywhere!! Thankfully, the water ran away from the basement instead of toward the basement...the clean up could have been A LOT worse. As bad as the outside bottom of the tank looked, the actual source of the leak was hidden. Here is the real culprit:
A blog by an Exclusive Buyer's Agent who is dedicated to buyer representation and protecting the rights of home buyers 100% of the time. I am a home buyers best friend!