I found a grounding conductor clamped downstream of an isolation valve and pressure reducing valve on a copper plumbing supply. The plumbing supply continued outside to an exterior hose bib. I traced the grounding conductor and it went through the crawlspace foundation to a grounding electrode burried outside the front door of the house. I am assuming there is a splice to the service panel bond with the neutral in the wall. Any idea why this grounding conductor would be attached downstream on a copper supply plumbing? Why is it leading into the direction of a ground electrode buried in the dirt outside?