Black copper cold water lines

Good morning all.
Yesterday I inspected a home that the copper cold water lines had turned black including the water meter. Only once before have I seen copper turn black to this extent. Coincidence or what, that home I inspected 2 years ago was 2 doors down from this one.
Can anyone shed some light on this.

Thanks Jerry

it sounds like a case of electrolysis, look for galvanized hangers pipe, or a nail in contact with the pipe. The chemical reaction between the two metals eat a way the copper pipe.

I agree with Ted. I had the condition a few years ago and the electrician was kind enough to call me and tell me what was going on.

Electrolysis effects the pipe at the dissimilar metal contact point. This homes cold water line was completely black. All the line that was not concealed about 20’ is black. I scraped the line in several different spots and found there to be no corrosion. A plumber friend told me it was caused from the cold water line sweating. I still have a hard time with this because all houses are not like this. I thought that maybe the furnace or hot water tank may be omitting carbon monoxide but I detected non and why only the cold and not the hot? Both hones I found this in were built in 1989 and bi-levels,so what?

Electrolysis can affect the pipe anywhere that it has electricity coursing through it continuously, as was the case with the home that I had inspected. Continuous electricity will cause copper to turn a very dark green or black.

Back in school the only thing that I remember turning copper black was sulphur. I can’t quite remember the chemical reaction to produce the reaction but I would look for something in that area.

Maybe a new type of meth lab??

I can’t quite buy into the electrolysis or electric current issue because of how we use copper to carry current. Open copper buss bars are everywhere with 1000’s of amps and no black

This is what inspection is all about – something does not smell right and could be an indicator of another problem


It’s a combination of many factors, including the fact that the copper pipes are carrying water, which the copper wires are not; the copper pipes are not insulated, which the copper wires are; the copper pipes are not meant to carry electricity on a continuous basis, which the copper wires are; etc. It might also have something to do with the quality of the copper, i.e., pure copper versus the alloys that are mostly copper.

I believe there has been some sort of chemical in the air that has done this . I think copper in a horse barn turns green from the Ammonia in urine . I wonder what chlorine fumes would do .
I believe some furnace manufactures list in their Furnace guide that the fumes from house hold cleaners can destroy the workings.

Roy Cooke A Happy NACHI member .

I did a search and as previously mentioned it is ( SULFUR will turn all lead colors black, also tin, copper, Cobalt, cadmium’s, manganese, arsenic and antimony)

Russel if you have electricity flowing through the pipe then why didn’t I get a shock?
Paul the water lines are not exposed to outdoor elements. If copper turns black with time then why don’t we see this all the time?
If its air quality then why only the cold line?
These are black not green and the black does not rub off in your hand but a light scrape with a knife or emery cloth takes it off.
I’m open to all opinions.
More puzzled than ever -Jerry

Hi Jerry,
It is the chemical reaction between the different metals that cause the electrolyzes. I have found this out years ago when I was contracting and my plumber had to re plumb an entire house because in the crawlspace there was a galvanized nail touching it.

I find it very interesting all the different opinions on this subject, the best one Was the meth lab theory. Sulfur could turn a pipe color but there would be sulfur in the hot and cold water not just the cold water and it does not turn the out side of the pipe black.

Check and see if the electrical panel is bonded to the plumbing, if it is check the bonding clamps copper pipe should be bonded with brass clamps and galvanized pipe should be bonded with galvanized clamps. When these bonding clamps are not correct I always call them out for this reason.

Lets look at RR’s thoughts on this

  1. A mixture of issues
  2. Current flow in the pipe – should not be a lot because ground should not have current flow unless something is wrong
  3. Type of copper -

Razors Law – Someone sprayed something on the pipes


I have been all over the web and I think I may have the solution. Both homes that had black lines had a water softener. I think the chemicals might have caused this. What are your opinions?


If you won,t take my advice on this than seek the advice of some seasoned plumbers you question has been answered, but you chose to disregard the answer, so you are now on your own. good luck. :roll:

I was going through old records and noted that I’ve had four homes that had black copper water pipes. On one home the electrician called to tell me what was going on, which was low currents flowing along the pipes. On the other three homes, which occurred after the first one and so I had that extra knowledge, we were able to detect low currents on the water pipes, and all four houses had a host of electrical problems. Until I find out otherwise, I’m sticking with the low electricity currents running continuously along the copper water pipes.

Actually, I believe I have an article around here somewhere concerning electricity and copper water pipes turning black. I’ll will endeavour (my Canadian friends should like that) to find it.

To Marcel Gratton:
Below is the response to Case No. 42438

Your question was: What would cause a cold copper water pipe to turn black?



Your contact for this case is: Tony Rakich

Key words there are “most likely.”

Sulfur, and most sulfur compounds, are easily detectable with zee ol’ nose, and if the concentrations are too high, can cause skin, eye, ear, nose, and throat irritation.

I’m sticking with electrical currents at low levels.

So this guy is stating that there was some sort of gas leak in the basement at one time?

What else can cause a sulphur build-up in the basement?

Maybe they had skunk issues?

I think Roy Cooke is on the right track. It is an atmospheric condition caused by sulphur.