Don't bother. Most pipes have some type of thread sealant applied between the joints (teflon tape, pipe dope, etc..). In effect, you might connect to the water pipe but how far that travels into the "ground" might be another story. Besides that, if your electrical ground is in another area of the yard, the difference between ground conductivity could create a ground loop and give you all kinds of hum or buzz problems or even result in what is known as a "hot chassis". Skip the "makeshift" installation and have an electrician run you a dedicated line. WELL worth it and much safer overall. Sean >