There's a technical reason why that happens, which is due to corrosion, but you can't tell from the outside of the unit. 

Copper pipe installed incorrectly in concrete (like many were years ago) have a corrosion problem.

I had the line cameraed and it showed that there is extensive corrosion of the pipes. 

The downstairs unit is currently on oil and the system is currently functioning but the tank has corrosion and the furnace is in rough shape.

There is also an issue with corrosion due to the moisture problem.In my opinion, these are structural issues that call into question the building's integrity.

t=484690Galvanized water supply is something I don't like, because the pipe is corroding from the inside, and eventually the corrosion can lead to blockage of the pipe.Iron waste pipe is somewhat more modern than alternatives like say clay ...

of the tanks were steel, and petroleum products are corrosive.

I think there are two possibilities: the brick itself, by some trick of composition and faulty firing, is susceptible to this kind of corrosion, and that something very weird is going on behind the brick.

I am born and raised in south Florida, University of Miami alum, BS & MS in Biomedical engineering and now working as a Sales Engineer related to coatings and corrosion (exciting topic, I know).  

If your water is not highly corrosive and the plumbing is reasonably accessible, and not leaking, I would leave it alone.