We have a corroded main water pipe that connects to a valve that goes into the house. The corroded pipe rises from the pave driveway and ends in a valve at the top.

Here's a picture: enter image description here

The building inspector said this could be caused by improper grounding? Is this a cause? What are some other causes?

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  • Where do you live, and how do you know the pipe is corroded? What do you mean by "rises from driveway" - is this the valve top or does the pipe itself go thru the air to your house? Commented Jun 13, 2016 at 13:11
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    Pictures in this case, would be most helpful. Commented Jun 13, 2016 at 13:44
  • If the paving is concrete, and the pipe is not isolated from it, that alone will corrode the pipe. Then again, exposure to water and air will also corrode a copper pipe (or roof, for that matter) and result in verdigris... how much corrosion there is determines at what point it's "normal" and at what point it's a problem. Indeed, pictures. If this is normal for your neighborhood, pictures of some neighboring pipes might prove useful, too.
    – Ecnerwal
    Commented Jun 13, 2016 at 13:54
  • Interesting info on causes of copper corrosion. I believe the OP must have been talking about external corrosion. Copper in contact with Concrete can cause corrosion or if touching any ferrous metals corrosion may occur. The last thing I can think of is strong cleaning agents used on cement / automotive cleaning could start corrosion. A clear lacquer spray paint will help eliminate corrosion, the pipe needs to be clean prior to application of the clear paint.
    – Ed Beal
    Commented Jun 13, 2016 at 14:24

1 Answer 1


Based on your picture:

  • Copper pipe in concrete; a problem.
  • Copper pipe connected to galvanized iron pipe (evidently) without a dielectric union; a problem.
  • Electrical ground connected to the galvanized iron pipe, not the copper pipe; likely also a problem, and would be a problem for the grounding if there was a dielectric union.

It is just possible that the union there is dielectric, in which case the copper above it and the ground wire above it are the main issues, but it's unlikely. A dielectric union is correctly used where the pipe material changes from copper to iron.

You could certainly start with a dielectric union and moving the ground wire (or having it moved by an electrician that knows what he or she is doing, unlike the one that put it there.)

  • That ground wire is for the cable system... I hope.
    – Mazura
    Commented Jun 14, 2016 at 19:33
  • Are you saying that the strap between the two flow controls is for grounding?
    – milesmeow
    Commented Jul 8, 2016 at 4:16
  • I don't know of any other reason to strap a wire to a pipe.
    – Ecnerwal
    Commented Jul 8, 2016 at 12:52

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