Had a call from a homeowner regarding blueish stains in the basins of a house I wired about 15 months ago.
She has a contractor friend that told her he had the same problem and it was "2 volts on the water causing electrolysis>
I have been burning up the internet looking for information about copper in the water supply and have learned a bit about cuprosolvency, galvanic reaction, and electrolysis.
What I find is that it can be very much a gray area with a lot of finger pointing.
I can't get out there until Saturday and I was wondering if anyone had any tips for what to look for so as to either prove or disprove that my installation is at fault.
I have read that having both ac voltage and current on the waterline with respect to the disconnected bonding conductor is normal but a dc offset could be a culprit.
I have also read that blueish water can be normal for the first year or so of a new copper piping system. I have read about low PH, high PH, oxygen content, and some other stuff that I can't remember now.

The electrical system is as follow:
A pole mounted 200A single phase overhead service feeding a 200A disconnect. 5/8" 8' ground rod at pole. 4 wire 3/0 copper feeders (w/ 1/0 EGC) ran underground 100' to a jbox that connects the copper to AL 4/0 SER (using NSI connectors) for about 30' to a 200A sub in laundry room. The jbox also holds the crimp on splice I had to make to extend the #4 bare copper GEC that clamps to the bottom bar of the footing rebar to the laundry room (no bond between neutral and ground buses). (I originally planned on the service being underground to the exterior wall and set up accordingly but that plan changed).
A #4 bare copper runs from the subs ground buss to the nearest accessible bonding point for both water and gas (they make us bond the gas here) which is about 20' away in the attic near the crawl hole.
The piping is all copper and run overhead (I seem to recall) except for about 15' ran under the slab to a kitchen island. I think it goes pvc before it enters the ground heading to the well.
There is a 20A solar system backfeeding a remote sub that was installed by a solar contractor. I also installed a tile floor heating system in the master bath.

What procedure would you use for determining if electrolysis could be the cause of the blue water?