I would speculate that the copper is coming out of the heater due to age, and possibly due to corrosive water chemistry at some point in the past. It also may have to do with what type of heater it is--I don't know much about them but there has been some discussion in the past about the newer models being much less prone to exchanger corrosion than the older models. At least you know where the copper is coming from and caught it before it became a problem. You could always use a metal-out product to keep the copper from staining....see mbar's sticky at the top of the "metal matters" thread.

Janet