On Wed, 05 Aug 2015 22:12:44 -0400, micky
wrote:

No, they last 10 or 20 years or more and there's no reason to replace
them early.


It depends on he water PH. I once lived in a house with well water that
was very acidic. It actually ate copper pipes, and water heater elements
had to be replaced every 3 or 4 years.

I worked for a guy who lived in a town that had very high calcium in the
water. In 3 years, his water heater was half filled with lime particles.
The lower element was buried in it. I tried to flush out all the lime,
but it was not possible. That 3 year old water heater had to be
replaced. Everyone in that town has that problem.

So, this question has no answer.....