In its simplest terms, the original galvanized piping was a continuous metal path from all the faucets and fixtures to the earth outside the house. When they replaced some of it with PEX, they broke the paths. You would either have to install "bridges" connecting both sides of the piping around the PEX, or provide an alternate means of reaching a ground. The gas line is "bonded" to the water lines to protect it in the case of a short circuit or lightning strike. That path also has to be continuous to an "earth/ground" point. In this area, even when the piping is copper, but the water line to the building is PVC, the electric panel has to be labled "Non metallic service line", and a mechanical grounding path established independent of the plumbing system.