Because of the previous leak eight or ten years ago, we believed the line from house to studio and then from studio to workshop was all copper. We found out today it's not.
One copper pipe comes from the house main water line. Somewhere between the house and the studio, someone at sometime or other split that line into two PVC (plastic) lines. The only reason to do this would be to have a separate water supply going to the workshop, which is behind the studio.
It would have made much more sense to have a single line go from the house to the studio and then from the studio to the workshop. But that's not how they did it. This means that the line going to the workshop runs UNDER the studio, and there's no way to access it or to turn it off if it springs a leak.
PVC should never have been used, not underground, not even in Arizona where the ground doesn't freeze. I have no (easy, affordable) way of replacing it, either. The current leak can be repaired -- it will require much more digging though far less actual labor to repair once the leak is found -- but future leaks are almost certain to happen, and sooner rather than later.
This is not good news. Not even.