Thoughts on the best safety protocols for stray voltage on a main water bond?

I had this exact thing happen on an old Square D service last summer. The homeowner complained about a tingling sensation when touching the kitchen faucet, and my Fluke 117 showed nearly 90 volts between the sink and the drain. What you're describing is a textbook open neutral. By disconnecting that copper wire from the water main, you cut off the only path your house had back to the transformer.

The flickering is happening becuase your 120V loads are now in series across 240V. Without that neutral connection, one leg might be seeing 160V while the other drops to 80V, wich will fry your electronics and fridge compressor in a heartbeat. Don't try to troubleshoot the panel yourself untill the incoming service is verified. Call the utility company right now and tell them you have a life-safety emergency with a dropped neutral. ussually, the overhead triplex has a corroded connection at the weatherhead or the pole. They will usually fix thier side for free, and it is much safer than poking around a hot panel while the voltages are floating like that. Once the utility confirms the service entrance is solid, then you can look at your bonding jumpers.

I wouldn’t be so quick to assume the break is inside your own panel or even on your service drop. A few years ago, I chased a similar ghost where we had 15 amps running through a 4 AWG copper ground bonded to a cold water pipe. We killed the main at the house, and the wire was still sparking. It turned out the neighbor three doors down had a snapped neutral at their weatherhead, and their return current was traveling through the city’s metallic water main and using our house's ground to get back to the utility transformer. Instead of just checking your own panel bonding, you need to pull an amp clamp on that ground wire with your main breaker turned off. If you’re still seeing current flow, it’s a utility grid issue or a neighbor’s problem, not yours. Disconnecting that wire was actually the most dangerous move because now your house has no stable reference, wich is why your voltages are swinging and flickering. You’re lucky you didn’t fry every piece of electronics in the house. Get the utility company out there imediately to check the street-side connections before your electrician even starts opening up your breakers.

Spot on about the open neutral. I've seen this happen where the current was so high it actually started pitting the copper pipe at the joints. One thing to keep in mind while you're waiting for the utility: tell that plumber to stay away from the water meter too. If he decides to pull the meter to swap it out without a jumper cable across the gap, he's going to get a face full of sparks becuase he'll become the only path to ground. When the voltages are floating like that, even your hose bibs outside can become a massive shock hazard.

This sounds terrifying. I don’t know much about electricity, but does this mean the copper pipe is actually acting like a wire for the whole neighborhood? If the neighbor has the broken connection, why is the power traveling trough this house's pipes instead of just staying at thier place? I'm also worried about the flickering—should we be unplugging everything in the house untill the utility company shows up, or is just having the main breaker off enough to keep the appliances from getting fried by fried by that wierd 240V thing?