I suspect the (electric) water heater. That is where I would start.

How about the house ground? Mine happens to be on the cold water side of the WH. I'm not sure, but you may need to tie the hot side to the cold side with a copper grounding wire since you now are using pvc at the tank.

Measure voltage between the faucet and a proper ground. In most cases, the voltage must be more than 5V to get a shock. Shut off power to the water heater and see if the problem remains. If it does, there is most likely some other electrical problem.
If it was the water heater, I'd expect current at all faucets connected to it. It is highly unusual for a new, properly installed water heater to cause such a problem, but not impossible, I guess.
Keep in mind that the current might be coming from the drain plumbing, not the faucet. So if you get no reading from the faucet to a proper ground, check the drain to ground.

j7r6s-
This post was interesting to me because of a recent experience I had. I gave myself a manicure last week, and afterwards was taking a shower. I had clipped a couple of cuticles too closely, and several times, while adjusting the temperature of the water I noticed a slight, painful burning sensation right where the skin was broken when that area of my finger brushed against the metal of the faucet. It didn't occur where there was unbroken skin. I figured that it was some type of galvanic action facilitated by the water. I didn't think much of it, other than that it was a little odd.

My house is 10 years old with copper plumbing, and the electrical system is to code. The shower is tile on a concrete slab in contact with the earth. After reading your post, I became a little concerned and got out my multimeter. I checked to see if I could get any readings -- AC or DC -- between the ground/neutral sides of a nearby electrical outlet and any of the metal plumbing spouts, handles, or drains in the shower, tub, and sinks. I got no readings. So, while I don't think I have a problem, I just thought I would throw this out there and see whether any one else wants to speculate on this "shocking" phenomenon.

"The shower is tile on a concrete slab in contact with the earth. "

The earth is not a very good conductor at 120 V.

The earth ground is not a safety ground so much as protection against high voltage leakage at pole transformers and lightning.

Once you get past the epidermis humans are actually pretty good conductors.

brickeyee (or others)-
I did a little more investigation. Any further observations are welcome.

Using an analog multimeter, I hooked one probe directly to the ground wire of a receptacle. I used the other probe to check all the metal faucets and spouts in the bathroom, and they all had continuity with the grounding. I then checked to see if I could get any readings between the metal plumbing fixtures and the ground wire...nothing on any settings at any sensitivity range.

Then I connected one probe to the shower faucet and laid the other probe on the floor of the shower, blocked the drain, and submerged the probe under an inch of water. This time I got some readings: slightly less than 1 V AC, 0.1 V DC, and about 20 microamps. I then turned all power off at the main breaker...and these identical readings persisted. I re-checked all of this with a different analog multimeter and got identical results.

So what are the possible sources of these stray readings? Or, more to the point, does any of this mean anything? All utilities are underground. I do have a security system with a battery backup that I think is grounded, as well as a fiber optic system with battery backup for phone, Internet, and tv. My hot water tank is gas-fired. The heating system is radiant with PEX tubing in the concrete slab. I noticed that there is a ground wire coming out of the ground by the gas meter, but that is disconnected.

(P.S.: I didn't mean to hijack the OP's thread, but there seem to be some similarities in the situations.)

j7r6s-
Do you get your readings with the main breaker turned off?

":slightly less than 1 V AC, 0.1 V DC, and about 20 microamps"

This levels are generally below detectability by humans and are so small as to be harmless.

There are numerous sources of stray current, starting with all the grounding electrodes at every service.

brickeyee-
Thanks. I thought that those readings were so low as to be a non-issue, but I appreciate the confirmation. I was just surprised that I was getting any readings. I know it is impossible to easily identify what specifically is causing that stray current, but I am still curious. For example, is it possible to get minor stuff like this from battery-powered backup systems (wired smoke detectors, alarm system, phone/Fios interface panel) that are tied in to the home wiring? Or can this also originate from outside the home?

My main concern had been if the measurements were indicative of a defect that could perhaps rise to higher levels over time. Does the fact that the readings are still present when I throw the main breaker tell us anything?

And finally, is there any point in pursuing this further?

Stray voltage is literally in the ground. Drive two ground stakes into the ground a few dozen feet apart and you'll usually be able to measure a voltage between them.

I wish I could go back in time to about 1750 and try that experiment.

"Issue 2: The home inspector indicated that the ground and neutral wires are not separated in the electrical subpanels of the home. I don't know enough about whole house wiring to know if this could contribute, but wanted to mention it."

This is likley the problem.

The grounding conductors and grounded conductors should only be connected at the main panel by way of the main bonding jumper.

Otherwise the grounding conductors can become current carrying conductors.

Start by properly separating the grounding conductors (grounds) and grounded conductors (neutrals) in all subpanels.

And if the condition persists, start looking for an open ground in the system....

"Otherwise the grounding conductors can become current carrying conductors. "

It is actually even worse than "can," they WILL be carrying a portion of the neutral current between the sub-panels and the main panel.

This can resulkt in very small stray voltages since the ground at the sub-panels is raised up in voltage by whatever the drop is back to the main panel.

If the grounds are kept separate their is no current flowing in them and no drop.

While the neutral will still have a small drop, the grounds will remain at zero.

Thanks for all of the replies. I didn't mean to stay away from the thread for so long. I did test all of the other faucets in the home with my multimeter, using the electrical outlet ground as recommended above. I do have low voltages on all of the faucets, 1.5 - 2 volts. I also tested with the water heater breaker shut off, and the voltage was still present.

I did get a couple feet of #6 copper and the necessary clamps to make a bonding jumper between the hot and cold water pipes at the water heater. I feel comfortable enough to install that, and don't think it could hurt anything even if it's not the problem. I haven't put it on yet.

I'm going to get someone to separate the ground and neutral lines in my subpanels. My brother in law is actually a commercial electrician, so I may be able to get him out to fix it.

I was the only one who could even feel the current initially, and then it was only with wet hands through a cut on my finger. I guess the broken skin provided better conductivity. My concern is that it could somehow jump above single digit voltages as I didn't understand why a water pipe would be charged in the first place. I'll let you guys know if the problem goes away with the jumper and the rewired subpanels. Thanks a lot for all of the input.

j7r6s-
I see you tested with the water heater breaker off, which was good. But did you try with the main breaker for the whole house off? That would, I presume, help determine whether this is an inside the house wiring issue or something external to the breaker panel.

And also post back after your next steps, too.

I suggest static shock. Some people are very prone to this. The key is that usually one person notices it but that others do not. Shuffle through the house in slippers,hop in the tub and walla, a minor shock. Women seem a little more prone to this.

texasredhead-
I am not the OP, but I did post here after this thread started because I was having somewhat the same experience as the OP. I thought about the possibility of static electricity, but the sensation occurred repeatedly every time I contacted the metal faucet without me moving around. If it had been static electricity, it should have discharged with the first contact.

In my case, I may have found the culprit. Two weeks or so ago I started to have trouble with a garage door opener and finally determined that the low voltage wiring running from the motor head to the IR sensors was shorting to ground. Whoever installed it ran it in a place where it was getting pinched by the metal bracket of a ceiling receptacle and it finally shorted out so that my IR sensors wouldn't communicate. I disconnected this wire and ran a new one. Now my garage door works and I haven't detected the mini-pricking sensation when I touch the grounded plumbing. I guess it's still possible that I was previously picking up some minor, stray ground current that's not present right now, and the garage door wiring fix is just coincidental. But, whatever it was, it seems to not be an issue.

What the OP is talking about is referred to as stray voltage. Google it and you will find tons of stuff to read. It's not static caused by a DC charge on your body, it is AC. I am a retired electric utility engineer and when I was working I saw it one time but I was at a loss as to what it was. I have since learned more about it. Utilities in dairy country are much more knowledgeable about stray voltage because cows are extremely sensitive to very small voltages. There is likely more than one cause but I believe the most common cause is a difference in voltage between the system primary neutral and your local ground. The primary neutral is probably connected over dozens of square miles if not hundreds. You can't expect the earth potential to be constant over such a large area. There are also voltage drops caused by current flow on the neutral which is caused by unbalanced load. I also believe you would solve most cases of stray voltage by bonding everything and not worrying about the voltage. A lot of european countries require all fixtures in bathrooms to be bonded. That is what is done in dairy barns.

hth,
Ichabod