How do I ground copper water pipes to old iron water pipes?

To connect iron to copper, you generally have to use a <a href="http://www.plumbingstore.com/images/copperfemaleadapter.jpg">threaded copper connector</a> at the joint. One side is a smooth fitting soldered to the copper pipe, and the other is threaded to connect to the iron. You can try to thread the end of your existing iron pipe, but it's generally "easier" to go back to the nearest elbow on the iron, put the new fitting there, and then run copper pipe to the new device. Bewarned, if the iron has been there any length of time, it may not want to come apart and may be thoroughly corroded inside...I've had old galvanized pipes simply crush when I went to undo them. You can also generally buy brand new iron fittings at most home centers, so you could simply pipe in the new filter using iron pipe. You will not be able to connect the two with solder, generally speaking, and get a good joint. By virtue of the two pipes being joined, they're already grounded. All metal plumbing pipework ...  more