Help! Attack of the pinhole leaks.

I'm with you, @ChrisJ . Further, no one seems to be following up on water quality... or exterior contaminants getting on the pipe, like cement dust...

As you can see it would take a troubleshooter with many skill sets to determine pin hole causes, plumbing, electrical, chemistry. Plus time and patience, and equipment to perform all the tests. And $$!

With water quality, it can change from time to time. Based on the source, the chemicals used at the treatment facility. Was the dosers out of spec for a period of time?

My city water report notes that the water numbers will change over the year. They now show a range for hardness, and other readings instead of a specific number. On other tests it indicates within EPA range, with no specific number?