Black copper cold water lines

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“Urine residue is a water soluble and extremely hydroscopic urea salt (its simplest form is CO(NH2)2). It can actually suck moisture right out of the air. When urea salt becomes damp, it reacts with its surroundings and produces a gas called mercaptan (A sulfur-containing organic compound with the general formula RSH where R is any carbon based radical, S is sulphur and H is hydrogen. Often ethyl mercaptan, C2H5 SH.) is the smell that we associate with a urine contamination.”

Above copied from:

Below copied from:

Hope this helps


20 feet of black pipe with cat urine?

Morning Guys and gals,
Within the next few days I am going to stop back at the home I inspected and ask the home owner about the chemicals he uses in his water softener. The water softener was located in the furnace room where the copper lines were most visible. I also am waiting for a response from a company that supplies and installs water softeners. Maybe I’m barking up the wrong tree but I will let you know if I find any grounds to support my theory. I’ve never seen a cat spray from floor to ceiling before but I’m finding out there are many things I have not seen before.
Keeping an open mind-Jerry
PS. When I said the water meter was also black, I didn’t mention it was brass.

That’s what I was thinking.

And considering that the pipe in my four units was about two feet off the ground in a crawlspace, the cat would have had to lay down on the ground, roll over, and shoot that pee like hell to get it all over every pipe in the crawlspace.

Nice kitty kitty.

I still haven’t heard a better explanation than what the plumbers here provided me.

Now that’s funny Kitty Ray!

Must be a Tom Cat because they have better aim and pressure, perhaps David could confirm…:razz:

Seriously though, my previous post did read that cat urine reacts with its surrondings and produces a


I noticed on my water lines they are turning black,just noticed the problem this morning.I just recently had the hot water heater replaced in November and now I have noticed the lines are turning black.Am wondering if this a coincidence or if this maybe relate.Any opinions or suggestions would be greatly appreciated.

Please check to see if it is a gas water heater that it is venting properly

Also check to see that there are no gas leaks

Me think it is not related to the new heater but to something else that has changed in the home

Why did the other heater need changing

If the new heater is electric is it pulling current through the cold water line?

Something might be wired wrong - this would also be related to poor recovery time

While many beleave that black water line are related to current flow I do not but it is worth checking

Current flow exists in copper in the electrical and telecom industry and the copper does not turn black, It will change color but not because of the current flow (to my knowledge)


Sound familiar?

I’m sure there are many other things that can cause copper pipes to discolor but one I know about is simply moisture.

A toilet constantly running causes the cold water pipe to be much colder than normal therefore cause it to sweat, especially if a basement window or such is open.
Naturally only the cold side pipes would turn black in that particular case though.

Who knows what chemicals have been previously stored in people’s basements or storage areas.

I carry lengths of new copper pipe inside of 4" PVC pipes on top of my service van and after a while pretty much all of them are black from being wet.
If it wasn’t so cold out and I wasn’t so lazy, I could go out right now and shoot a picture of new copper pipe that is black from carrying it around.


Perchance do you have a dirt floor in the basement?

What type of softener is in the room? Salts of any kind react with copper to speed up the discoloration (whether it is natural or chemically modified). Whether it is Electrolysis or chemical (such as sulfides) the environment is the key to the color.

Copper naturally reacts to its environment and goes through a weathering progression, the rate of which is related to its degree of exposure to moisture, salt and atmospheric pollutants such as sulfur. In some arid climates, it will mature to a nut-brown or ebony-like patina. In coastal or moist areas, the patina will progress to variations of a grayish-bluish-green. Usually, within 10 years to 30 years, copper will reach a weathering equilibrium where the oxide film stabilizes and no longer changes color; however, it continues to protect copper from aggressive corrosion attack.
(From Professional Roofing Magazine)

When I read about galvanized steel to copper contact, the experts always seem to say that the galvanized steel is the one that will corrode. However that has not been what I have seen. What I see many times is that the copper pipe turns green where it makes a ground connection.

One of my most important rules is - Alway try the easiest things first. (because you will feel like a fool if you tried the hard stuff first and it turns out to be the easiest thing)

Maybe the cold water pipes were colored black to distinguish them from the hot water pipes.

Old post here but I inspected a home yesterday with black copper supply lines throughout the basement. There was a water softener in the basement.


But, interesting (and informative) post.

Surprised that the chemical theory wasn’t dismissed because the OP only had one set of pipes that turned.


To preclude theft, I have seen many homeowners paint the copper black.

haha, now there’s something I never thought of. However I have the feeling the typical copper thief would know better than to pass up the apparent gas lines. Last night I inspected a vacant home with copper drain lines. All I could think about was how a scrap thief would be drooling at the sight of it.

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I had this question once.
Noticed when going thru art fairs that certain coppers would turn black ,while others did not.
Never got a total straight ,one fits all,but it may be the metal itself,as I have seen it effect sections,while others kept color.

Personally ,I never comment on it in a report.

The cold water pipes collect condensation more than the warm pipes.
The water softener might add to the humidity, i don’t know.
The other ingredient is dust, which sticks to the wet and forms a black crud layer.
I wouldn’t give it much thought beyond that. :stuck_out_tongue:

John Kogel