The building is a townhouse, 4 stories, a basement apt. with the problem and 3 floors upstairs. I know the voltage was there when we turned off the apartment main. The apartment gets one electric bill, the upstairs a different metered bill. We did not try turning off both mains. We will try that. I have never seen a spark, and I can’t feel the voltage (5v). The house was built in 1901, so metal, not plastic pipes from street. I looked where the water cut-off is, the pipes appeared to be galvanized not copper, and a wire aimed in the direction of the electric panel passing behind the drywall seemed firmly clipped to the water pipe. Any other ideas?? Anyway, thanks.
This is not my line of work, but have been down this road.
We live in a 100-year-old house, when we moved in the refrigerator had a similar problem.
I upgraded to 3 wire receptacles and added a ground wire to the back of the fridge GROUND SCREW, did the trick.
The main tool I used was a Greenlee GT16 noncontact voltage tester. *Note the model goes to FIVE VOLTS, many others only read near 110 volts.
https://www.greenlee.com/products/ADJUSTABLE-VOLTAGE-DETECTOR.html
I check the voltage tester before EVERY USE by rubbing it past my sleeve or the carpet to see it light up.
Guessing that somewhere there is a ground fault, I had the fridge and an old desk fan.Upgrading to 3 prong receptacles that were properly grounded was the answer.
I did the work slowly over some time.Checked the work with an inexpensive tester:
https://www.homedepot.com/p/Power-Gear-3-Wire-Receptacle-Tester-50542/206212329?cm_mmc=Shopping%7CG%7CBase%7CD27E%7C27-11_TOOLS_%26_ACCESSORIES%7CNA%7CPLA%7c71700000034238984%7c58700003943782712%7c92700031954542185&gclid=CjwKCAjww6XXBRByEiwAM-ZUIABo9CR69SvEPVdvwmER08TVbsTrEzktIHKid7dpVaUIArjpRIXm6xoCkrgQAvD_BwE&dclid=CMqLiPqr59oCFUOUaQodcSMI-g
My retired cousin did her entire old house while her husband was working out of town, slow but sure.
One reason some people feel it is called skin resistance some have dry skin and higher resistance to the flow of electricity.
Try grounding the faucet from underneath the sink to a clean metal pipe. sand the pipes to shine them with sandpaper,use ground clamps and copper wire.
Clamps like this one: https://www.grainger.com/product/2DDE7?cm_mmc=PPC:+Google+PLA&s_kwcid=AL!2966!3!166591489617!!!g!137372519842!&ef_id=WtdOrwAAAH85oxA0:20180502153458:s
Further thought, while the pipes coming into the building are galvanized, there was considerable renovation before we bought the house in the early 1980s with the (not original) English basement probably put in at that time as has/is being done with other houses in this row. The interior pipes are likely to be some sort of plastic. Will have to look under the sink, etc.