This
iron pipe was used to fill the difference between the copper pipe and the
hot water heater. It was a few months old at the time of this photo, and was
already oxidized badly.
The process, known as the galvanic reaction, is where two dis-similar metals (here, copper and iron) are connected with a path for electrons to exchange. The flow of electrons causes rust. Think of the sixth grade potato-clock science project. In this case, the water softener was pumping salt water through the pipes, easily allowing electrons flow from iron to the copper. This leaves the iron with a negative charge, and it attracts oxygen. Yep, the handy man responsible for this one just turned the hot water heater into a battery, and didn't even hook it into the breaker box.
We're
pretty sure that 'Christmas light extension chord' isn't approved for in-wall wiring. This
wiring ran two lights and a switch. We salute the duck tape chord wrap. Actually
it's very dangerous.
However, the plumbing here was actually the reason for taking this pic. When you enlarge, notice the brass elbow on the lower right. This was genius. To be clear, the shower valve was already in place. The down pipe coming up from the bottom had to be soldered to the elbow first, to avoid burning the Teflon tape that had to go on the threads of the horizontal pipe on the left (follow me). Then the whole assembly was screwed/threaded together on the right. We'll let you think about that for a while. Notice the 2x4 that would have been in the way.
This is great.