Mild Electric Shocks in Bathroom
Sounds like you have an improperly bonded neutral somewhere. If it isn't easily identified at the main service panel, you'll want to do a couple of things:


Call your electrical company and request (or if necessary demand) that they check to make sure the incoming neutral wire is grounded correctly on their side of the service. 
Make sure that the water service to the house has a grounding connection to the ground bus of the panel within 5 feet of entering the house and before the meter. 
Install new grounding rods to ensure that they are providing an adequate ground.
Install jumpers around any dielectric connections in the plumbing.


If none of these steps solves the issue, I'd start opening things up and make sure that you don't have a crossed neutral and ground somewhere in the house.