I was washing dishes yesterday and as I was approaching my wet hand to the water tap, I felt a tiny jolt on my finger. I repeated the motion and each time I would feel the jolt.
I took my voltmeter and put one terminal on the metallic sink and the other on the tap and there indeed was a voltage difference of 0.6 volts
Where is this voltage coming from? I suspected the electric water heater, but the voltage is still there even when it is turned off. Also, 0.6 volts isn’t going to kill anyone but could the voltage increase? Should I have it checked?
Your wiring system is probably grounded to your water supply piping. You have some device that is feeding current to the ground. Try isolating circuits until you eliminate the voltage, then check each device on that circuit.
0.6 V is not nearly enough for you to feel even with wet hands, as it’s well below the threshold of sensation. Chances are the metal sink tub is not grounded–your meter will probably register that much if you simply touch one lead to the tap and let the other one hang in the air, assuming it’s a digital. You need a ground reference for a meaningful voltage measurement. If you have an three-prong outlet nearby, you can try a measurement between the tap handle and the third, grounding, prong.
There’s no doubt that there is a voltage difference between the tap and the sink. I touched both prongs on the sink and then both prongs on the tap. In both cases the multimeter showed zero (as it should).
Also the taps come from the wall and the sink has a about 1 cm distance from the wall so there is no contact between them.
There’s no garbage disposal, dishwasher or any other electrical device apart from the water heater AFAIK.
I don’t know how you felt 0.6 volts, perhaps if you have a open wound. But I’d suggest testing the voltage with and without the main circuit breaker thrown to see if it’s a issue with your electric service (as 0.6 volts is very small and can be caused by other things even dissimilar metals.
This isn’t probative; it only shows that the tap handle and sink are not at equipotential. Touch one probe to the tap handle and let the other hang free, as I previously suggested, and tell me what you read. If possible, install a (~1k Ohms) resistance between the tap handle and the sink and take a reading again. I can all but guarantee the apparent voltage disappears. Which is not to say there isn’t a real voltage present on the tap handle, but measuring it against the sink, which is almost certainly electrically isolated from everything (except possibly from the tap handle itself), is not going to tell you a thing. To be certain, measure the resistance between the sink tub and the tap handle, and also between the sink tub and Earth ground at a nearby outlet, as I outlined previously. If both readings show infinite, or nearly so, resistance then you know there’s no circuit path there.
Suspicion: Both the faucet and the basin are probably connected to something, somewhere, but there may be a very long path between them. A bit of improper wiring somewhere in the house could be feeding voltage (possibly dangerously high voltage) into some point on that path, nearer to (without loss of generality) the faucet than to the basin. So both the faucet and the basin are “hot”, but due to resistance in the pipes, there’s a small voltage drop between the faucet and the basin.
The fact that the faucet and the basin are very close (.6 volts) to the same voltage does not mean that either of them is very close to true ground, and in fact the fact that you felt a shock is evidence that they are not at true ground. Without knowing what’s causing this, you can’t say reliably whether it might get worse. This is a potentially dangerous situation, and you may not have the necessary tools or expertise to diagnose or fix it. Call a professional electrician.