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I just noticed some green corrosion around the shut off valve area under a bathroom sink. This is a new shut off valve that was installed by a plumbing company only around a year ago. Should I have them come out to re do it?

  • is there any indication of a leak at the joint? This level of copper oxidation is often the result of a wet joint or low spot accumulating water drips.
    – mark f
    Oct 17, 2020 at 14:29
  • 1
    There is a dried green dot right under this area. My thought is there was maybe a very small drip that caused this build up and now the corrosion has sealed things off perhaps.
    – user109773
    Oct 17, 2020 at 15:31

2 Answers 2


It may simply be condensation on a cold water line. The rule of thumb in plumbing is if the joint isn't leaking don't eff with it.

  • Think of it as a feature of copper alloys. Metal loss would be nearly impossible to measure ( It would require removal and laboratory testing). Oct 17, 2020 at 16:08

Perhaps excess acid flux was not wiped off. Vigorously wipe the area with a wet paper towel and see if the green deposits come off. If they don't, then rub with a terry cloth rag wetted with hot water. Probably the green will not return.

  • 1
    Pretty clearly a threaded connection.
    – Ecnerwal
    Oct 17, 2020 at 16:28
  • I saw signs of threads, but in my (limited) experience all shut-off valves are connected to the house supply by sweated or compression so I decided not to believe my lying eyes. Oct 17, 2020 at 19:46

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