How can you ground an ungrounded electrical outlet to a cold water pipe?

It is true that a cold water pipe will work as a ground but it should not be trusted. If the wiring in a house is older then the introduction of electrical grounding I would have to recommend the instillation of new grounded wiring. Grounding using the Plumbing system, past where the cold water pipe enters the house, can present a hazard to plumbers. They can receive electrical shock if they remove a piece of pipe that was part of the groundings pathway. Also, as plumbing codes change they do not take into account electrical need. In many areas of the united states plumbers are using non-metallic piping and fitting. If this is added to your system you will lose your grounding.