Years ago I noticed that my hands would occassionally tingle at my kitchen sink. It soon became apparent that my refrigerator handle also have a funny feeling. This feeling was pronounced when I was using either, while sneeking across a freshly washed floor. It all made sense later when I was pulling out the refrigerator and the cord shorted out. The new refrigerator went in and my problem went away. I suspected that there was a trickle short through the refrigerator and into the bonded side. The refrigerator must have been acting as the resistor and therefore didn't allow enough flow to trip the breaker. (Then came gfi)
Your hot water heater (220) uses the neutral (white) wire to ground the heater back to the panel. The panel should be bonded (grounded) to either a grounding road and may be attached to your old iron pipes. You may have a ground fault condition. If the faucets are tingling, and your pipes are part of the grounding system, I suspect there might be something on the bonded side of the system. If removing the ground you installed to the pipes takes away the tingling, DO NOT assume the problem has gone away. Have your grounding and panel checked out.