Sorry, I didn't explain well. I wasn't discussing code complaint grounding. I was speaking of stopping corrosion at the fittings. I'm no kind of physicist and not a good teacher, so I'll try to explain what I've learned in school & many corrosion control classes.
Even if the piping is all plastic until it gets to a grounded point, the minerals in the water will stave off much corrosion by providing a path to ground for the electrons that cause corrosion of dissimilar metal. The minerals touch your metal fittings and carry a small amount of current in the water until it reaches an earth ground.
Try this experiment: Take a thremocouple. Connect a DC milivolt meter to the thermocouple. Heat the thermocouple and see the voltage, about 75 mv. Now take a wire with two alligator clips & attach one to the thermocouple's wire and clip the other to a metal water pipe that is interrupted by plastic somewhere between where you connected and where the piping is grounded (service entrance). The meter will show lower volts. This is because the minerals in the water- even inside the plastic pipe- carry the same electrons that will let the oxygen in the water start corroding fittings safely to earth.
If you could do the above with distilled water, the meter would still show the same 75 mv. Why? No minerals in the water to carry the current to earth.
Next, screw a piece of steel and a piece of aluminum together tightly. Drop one on a plastic bucket of water. Drop one in a metal bucket (paint can) and attach the can to any metal pipe. Leave them for a week. Upon disassembly, you will see corrosion starting between the plates on the plastic bucket model & none on the metal bucket plates. Same action takes place with copper and steel, but more slowly. It will take hundreds of years if steel and brass are plated together because the zinc in the brass sacrifices itself.
With corrosion control, grounding is key.
You did the proper thing by installing two rods, at least 6 feet apart, to serve as grounding electrodes. Rods, plates or many other are acceptable as outlined in the code if built and installed correctly.
In jurisdictions covered by NFPA 70, water pipe is no longer allowed to be the supplemental ground unless the connection is within 5 feet of the water service entrance and is all metal not aluminum and is visible and has at least five feet of buried pipe outside or under the building. Plus, in many cases the conductor to the pipe has to be in grounded rigid or IM conduit with bond bushings. So, you still probably need 2 electrodes, 6 feet or more apart and connected by an unbroken conductor, with some splicing exceptions. (Six feet apart is so the eddy currents don't collide and allow a circular path, negating electron flow to earth.)
Actually, most locales where I worked, and the one where I was an AHJ, two electrodes were required, no matter the piping. (Note- I'm retired & don't attend code update classes. Things may have changed.)
I doubt I did, but I hope I explained well.
PS: Sorry for late reply. I don't get reply notifications anymore from plumbingforums. Beats me why.
