At one time it was a common practice to ground the electrical system by connecting it to the nearest copper pipe. This is no longer acceptable for obvious reasons.
Copper pipes are often grounded to a grounding post outside, so there might be some residual voltage escaping a device. Check to make sure that the pipe is grounded, which is usually near the main house valve.
Most likely your service entrance ground is connected to your copper plumbing. This can be resolved by installing a ground rod and re-routing your ground wire outside.
I would believe that you have a shorted out electrical wire some where in your house, or an open/ exposed live wire that is touching the copper pipes. Copper is an amazing conducter of electricity.
