You've checked all the obvious, not it's time to check the unobvious. I've worked for 35+ years in the aerospace industry, much of it designing/manufacturing missiles and bombs. We take static electricity and grounding very seriously, it's not just comm problems or missed steps, it's someones life when it static happens where it shouldn't. That being said, I recommend three things.
First is, I think you and your electrician are very mis-informed about grounding rods. It sounds like you have more than one rod in your overall system. Is your machine electrical grounded via your building electrical system? Do you have a completely separate grounding rod just for your dust collection? If yes, that's a big problem. You have created electrical potential between the two grounds which can can all kinds of issues. Just use your the ground that your machine is electrically connected to. That way the operating computer, the control box, the machine structure, the router or spindle and the dust collector are all connected to same ground with the same potential.
Second, pouring water on the ground rod is ill-informed. The soil has minerals in it, the water that you're adding either has minerals and chlorine or salt and chlorine in it. You are causing the soil to leach minerals towards and onto the grounding rod. Think how electrical plating or chroming works. Once enough minerals have attached themselves to the rod conductivity to the soil is significantly reduced. Depending on your soil this can happen quickly or slowly over time. Copper does not rust but I'm sure you have seen it "patina", that is simply chemicals and minerals changing the surface structure of the copper and making it less conductive.
Third, you may think that everything is connected and grounded, but you need to actually test it for conductivity. Use a DVM (digital volt meter) and check for continuity between all the components of your system (building electrical ground, computer, control box, machine frame, machine gantry, dust collection hose or piping, and dust collector).
Hope some of this helps.
Jim
Jim
96 x 60 PRSalpha, 5HP Colombo spindle, Custom indexer, Custom vacuum table, Custom Fire Extinguishing System