All water heaters have electrolysis with copper plumbing. The tank is
steel and where it connects to copper you have electron flow. That's
why you should install a dielectric nipple between the two. Years ago
they used dielectric unions, but the nipple gets you about 3" of
Also, copper can wear whenever there's excessive swirling going on.
Plumbers are busy these days replacing copper in 50-year old
buildings, expecially near 90 degree fittings. That's where you find
the most swirl. It's worse if the plumber used too much solder and
there's a bead of it inside the fitting--makes the swirl even worse.
Turns out copper piping isn't the wonder material everyone thought it
was. It's still better than galvanized though. And who knows when
we'll start seeing problems with Cpvc.