Water in an old building, tested recently, showed high copper and iron content, and low pH levels. A water reading taken 20 years before showed low pH levels, but only minimal traces of copper and iron. If none of the new buildings on the same street showed signs of metallic contaminants, but all reported lower than normal pH readings, how might these readings be explained?

The older buildings posses the older pipes, when the pipes get older they get rusty as well as corroded. These pipes are likely to release copper and iron ions to the water supply of the old building. This imparts acidity to the water and hence, the pH is low. The newer buildings might have newer pipes, so the release of copper and iron will be in trace amounts or negligible in the water supply. Thus the acidity will be lower in water and also the pH will be normal.