Does anyone know what this green stuff is here

It has a paste like consistency.

Pretty sure that is isn’t oxidised copper as there it is too thick/ there is too much and none is on the copper pipework.

If anymore information is required let me know.


The green stuff is cupric chloride, a byproduct of corrosion of the valve body. It's typical of water leakage where the water is of low pH. It's usually found on copper pipes. Your pipes have been painted so it's not forming on them but you do have untreated copper going into the valve. Make sure all the connection are tight.

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  • There are unpainted stretches of the copper pipework that have no discloration, is it likely to all be internal to the pipe and only visible at the joints? If so, as this leads to my kitchen tap, is the water from these pipes still safe to drink? – 123 Jan 25 at 13:28
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    It's totally safe to drink the water from all the pipes. Your painted pipes are not the norm, most are not painted. It won't be internal to the pipes. It was probably caused by a droplet of water that seeped through before sealing completely and it's on the outside of the valve, not the inside. – JACK Jan 25 at 14:19
  • Accumulation of condensation can aid in this happening too. – Jack Jan 25 at 17:31
  • So just clean it off and alls good? If you look at the image, theres is also some on the plastic coupling, so is it possible the pipes were compromised prior to being installed and some rubbed off? – 123 Jan 25 at 17:33
  • @123 Yep, clean it off and all's good. Keep in mind, as Jack pointed out in his comment, that condensation can cause this too. The pipes could have had some of it when installed but "compromise" is way to harsh.... I have all over some of my pipes and have never cleaned them off. – JACK Jan 25 at 17:51

There is a chance it is the glue (or cleaner) used for PVC pipes. There may have been PVC pipes previously installed and it dripped there. The part might be secondhand also, quite common with fittings. But it should be dry if glue, not paste.

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