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topic 24664

Copper pipe electrolysis from touching galvanized steel?

A discussion started in 2003 but continuing through 2020

electrolysis in copper pipe

Q. I recently had a 1/2" TYPE L HMP flexible copper pipe that sprung a leak, unfortunately it was inside the wall going up to the second floor. After splicing the pipe where it was leaking another spot started leaking. I noticed inside the pipe a bunch of green "blobs" & the outside of this (HOT) water pipe a lot cleaner than the other pipe (COLD) that would have been put in at the same time, 20-25 years ago I'm guessing. I did notice one spot where the copper pipe was touching an old galvanized pipe seemed to be wet and green. Could there have been some electrolysis going on that caused this pipe to start getting finer than pin hole leaks & how much damage might have been done to the rest of the plumbing if that is the case?


Alex H [last name deleted for privacy by Editor]
do-it-myself-er - Cedar Rapids , Iowa


A. Copper pipes can corrode in at least three different ways, but the differences are quite technical. I would suggest that the corrosion could be induced by a galvanic couple caused by contact with the galvanised pipe and this results in an induced local anodic polarisation of the copper pipe. I would normally expect such a failure to occur where the two pipes come into contact, but if this point is dry, no corrosion will occur and the effects of the galvanised pipe will be transmitted onto the copper pipe where it will react in a more favourable wet environment. Your photograph clearly shows the green copper salts on the inside of the failed straight pipe, so it must have been in an area where the copper is oxidised and failed. The propensity for copper pipes to fail is related to how the pipe was made, the local water composition and the environment it is used in. I would suggest there may be other not be other problems with your copper pipes, as there has already been a failure of an induced polarity, but if there are other non-compatible pipes in contact with each other, there could be a repeat of this. It may be wise to ask a plumber to check your system out.

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK


Q. I was told by a local plumber that electrolysis can occur in copper pipes when the hot water heating system is part of a forced hot water boiler system. The solution is to put nylon fittings between the copper connections and the galvanized boiler system so as to prevent any electrolysis action from taking place in the copper pipes running throughout the building. I would like to get other opinions since this is an expensive fix and it takes a long time to determine whether the fix in fact works.

Dan W [last name deleted for privacy by Editor]
property management - Juneau, Alaska


A. It is the right advise, Dan. For galvanic corrosion to occur you need a metallic circuit and an electrolyte circuit. If you break the conductive metal circuit between the copper and galvanized pipe, galvanic corrosion ("electrolysis")" does not occur. This is not to say that no form of corrosion will ever occur though.

Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha


A. Copper pipe failure began to occur approximately eight years after completion of a new home in Brewster Co. Texas. The leaks were always in the cold line.

A split-core ammeter revealed a slight current flow between the steel gas pipe and the hot side of the copper system. No current could be detected between the cold copper pipe and the hot, or the steel gas line. This led me to conclude that the cold line was acting as a sacrificial anode between the other two while absorbing all voltage drop.

No electrical bonding could be found.

My solution was to isolate the steel line (which included some galvanized parts), from the copper system with a PVC adapter.

Current flow cannot now be detected unless a jumper is placed between the steel and copper.

Is the problem solved? I don't know! What can be said is that there is no further measurable evidence of electrolytic activity in this particular system.

Sam D [last name deleted for privacy by Editor]
- Alpine, Texas


A. As others have mentioned, there are three different ways for holes to develop in a copper line, and I have seen all three.

A typical trade mark of electrolysis is pit on the inside of the pipe where the electrical current has actually eaten away at the piping, this doesn't sound like what is going on.

Another way is corrosion from the outside, normally when the piping in in a damp location with high acid soils, or even in an unsealed sleeve (copper run inside another pipe, usually PVC, and normally from the meter to the house). This is evidenced by pitting on the outside of the pipe.

The last one I have come across, and am still researching, is what it sounds like this gentleman has. It typically will have build-up on the inside of the piping and will often times leave large "blobs" of build up. I don't know what this is for sure, but I do know it isn't electrolysis, and it has nothing to do with water that is too clean (mentioned on another website as a possible answer). I think it has to do with the water quality to a certain degree, but I think it may be the molecular structure not the chemicals used. I think the buildup is a protectant for a "micro-atmosphere" high in maybe hydrogen. But I could be wrong, I am still researching this. I will post any further findings.

Jereme Grisenti
plumbing - Blountville, Tennessee


Q. If we were to rivet or otherwise attach a copper sleeve to galvanized chimney pipe, would this cause the galvanized pipe to fail? We have fireplace chimneys on the beach. we have several copper clad chimneys that are doing well, but the maker went out of business. Now we have only galvanized pipe to work with and the outside of it corroding causes an eye sore.

Bryan Malt
- San Diego, California


Q. This is a piggy back question.

Three 1/2 inch copper pipes running from my basement to the Laundry room one floor above show the same kind of erosion as the picture accompanying the original question. In each case the green copper salts and pin holes developed where the pipes pass through the floor. You can see the leaking water from below but not from the laundry room level.

After one of two plumbers to replace one of the leaky pipes stated that at one point he felt a very mild electrically shock, I had an electrician check the system. The electrician said he could not find a problem. The electrician checked the system before and after the plumber felt the shock. We could not duplicate the shock with the plumber or the electrician.

The plumber reinstalled the three pipes and wrapped the new pipes in electrical tape at the point where the pipes go through the floor.

Since we have not yet found a source of electrical charge would it be prudent to ground the copper line to an unused galvanized pipe so any current would flow to the unused galvanized pipe? Any help would be appreciated.

Greg Butts
- Stafford, Virginia


Q. When copper pipes are plastered over into walls do they need to be protected from corrosion either by cement or plaster?

Mrs M Bridger
Homeowner - Steyning, West Sussex, England


Q. I have a brick wall in my bathroom and want to cut a groove in the brick run the copper pipe inside and cement it back up. Will this have a long term effect on the pipe
thanks daz

Dario Ruberto
designer - Toronto, Canada


Q. I have some questions regarding electrolysis, or galvanic corrosion between the copper and galvanized water pipes in my house. The house in on a municipal system and it is my understanding that acidic or soft water is not a problem in my area.

I have extremely low pressure in the upstairs bathrooms, and moderately low on the main floor kitchen. In my basement I have galvanized pipes coming in from the street, they supply the hot water heater, and they run the hot water for a few feet beyond the tank. At one point they are connected directly to copper pipes which take the hot and cold supply upstairs to the bathrooms.

I intend to replace the galvanized pipe, but I am trying to decide whether or not to replace the copper pipes going upstairs, and as well the hot water heater.

To make this decision I need to understand a little more about what is going on with the electrolysis. Before discussing the ramifications with the hot water heater, I have the following questions:

1. Where the galvanized and copper connect in the basement, does the electrolysis happen only locally? It seems that the electrons would travel only within the magnetic field created by the metals and therefore only affect the pipes within about a foot or so of the connection. Or, since the water exists through all the pipes, does the electrolysis affect the copper all the way to the upstairs bathrooms?
2. Once the galvanized pipe is removed, will the electrolysis cease? (I understand that new copper and old copper will also create electrolysis but I assume this condition is not as severe.)
3. I understand why galvanized pipe corrodes when coupled with copper but I don't understand why it is that the galvanized pipe becomes filled with gunk on the inside and restricts flow, I would think the corroding would make it get slightly wider on the inside, not more narrow.
4. If I remove the galvanized pipe, can I clean out the remaining copper pipe to make sure there is no corrosive material setting in them? How is this performed?

As far as the hot water heater is concerned, galvanized pipe feeds it and takes the water out of it, however, there is copper flexible tubing that actually connects directly to it. I assume this means the heater has corrosive material in it and will likely not last as long. If I leave the existing heater in place and wait for it to fail, will it contaminate any new piping that I put in?

Also, if I run the new copper water service through the front yard within a few feet of the gas line will this cause electrolysis? If yes, will it affect the pipes inside the house or just in the front yard? Which pipe will get holes and which will narrow? Can I insulate the copper to prevent this?

Justin Zavislak
buyer, hobbyist - Seattle, Washington

July 13, 2008

Q. I have type k copper coming from the main to the shutoff in the house. after reporting a leak it was dug up to be repaired and all was found was a pipe with walls that have thinned considerably and covered in grooves resembling termite damage on wood. it was also riddled with pinholes.

the ground for my electrical is connected to this pipe. could that be a possible cause. please help. there other houses in the area that have had there lines replaced twice in the last 20 years.

thanks, cy

cyrus lambert
hobbyist - conne river, Newfoundland, Canada

July 20, 2008

A. Where I work they were having problems with the copper pipes. The anode rods in the water storage tanks had been all wore down. Plumbers found the electrical system grounding rod had been disconnected & everything was grounding through the plumbing, causing the problems. You might want to check but I think it is a code violation now to ground through your plumbing only.

Alex Hatfield
- Cedar Rapids, Iowa

August 30, 2008

Q. I have a problem identical to to the lead in this thread. Green spots on rigid type L 1/2 in copper pipe with water seepage. This 14+ ft run of pipe is leading from my gas fired hot water heater (after a few short copper fittings) across the drywall finished basement ceiling to a T that feeds hot water to most of the house. I noticed a small spot of mold on the ceiling, cut it open and found this pipe with green spots like the picture above and two of the spots (at different ends of this one section of pipe) have water seepage. There are several other copper pipes , cold water and feeds for hot water heating that have no green spots,(only this one length of hot water has the spots) and also a flexible gas line in the same bay. My fix is to replace this entire length. A difficult job for me, tight spaces overhead, and hope there are no other bad pipe in the house. Please confirm the cause of this. Is it likely to be elsewhere or reoccur?

David Goldman
- W Milford, New Jersey

September 3, 2008

A. In response to the gentleman who experienced a leak on a 1/2 copper pipe and then he split it exposing this thick green blob running on the inside for some unknown length. well from dealing with similar repairs and from years of experience in the field this green corrosion that you are talking about stands far from electrolysis. this green gunk/blob is what we use to solder/sweat our copper pipes with better known as FLUX this product is applied to the outside of the copper pipe once it has been cleaned and reamed. putting too much flux on the pipe and fitting will cause the excess to flow into the pipe and will settle on the inside of the pipe until the system gets energized and water flows flushing out the excess flux. if it was not flushed out and was left as is; guess what? call your plumber.....thanks.

Armando Olvera
- Costa Mesa, California

September 14, 2008

Q. Within the last 9 weeks we have called the plumber 3 times regarding a 4 ft. section of hot water copper piping. Each time a pinhole sealing leak about 4-6 feet away from a recently replaced(5 months ago that our plumber installed) electric hot water heater. After replacing 2 inch copper pipe sections at a time we finely asked him to change a length of pipe but, only last night we developed another leak, a foot over from the new pipe, closer to the water heater. Our house is 15 years old and we use city water. The leaky pipe had green discoloration at the leak points. The plumber says this problem could be expected in this area in homes using well water after about 20 years due to the highly acidic soil but we use city water and our pipes are in the sealing. He's suggesting we may need to replace all of our pipes but it seems strange that the leaks are all near the water heater. Could the water heater be faulty or it's installation be the problem?

Chris McQuillen
homeowner - Crescent City, California

September 14, 2008

A. Hi, Chris. I'd be pretty confident that is has to do with something electrical rather than well water. I think I'd call an electrician rather than calling the plumber again.


Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha


affil. link
Dielectric Union

September 30, 2008

Q. can a copper water line be spliced to an existing galvanized water pipe line?

Keith Medved
- Dyer, Indiana

A. Hi, Keith. When you transition from one kind of metal pipe to another, the correct thing to do is to use dielectric unions =>

These are unions that include a plastic insulator so there is no metal-to-metal contact. I'm not saying that this is always done, but it is the right way to insure that there can be no galvanic corrosion.


Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

October 24, 2008

Q. How can one determine the cause of frequent deterioration of a 3/4" copper water supply line? The section going bad is located underground at the block wall of the foundation. The home owner had to replace this line two times within the past year. The deterioration seems to occur on the outside of the pipe. There were no problems prior to the first replacement of this pipe section 9 months ago. The home has city water and uses a sump pump due to a high level of ground water. I don't know the pH level of the water. The basement is dry, but uses on a "floating slab" to channel away the ground water. I conducted load tests of the electric panel to verify the electric wiring. All tests proved satisfactory with only about .2 amps or less flowing to the ground wire. This is when a 35 amp load is applied to each 120 volt leg. This proves that practically all current is flowing back through the neutral conductor. The electric service is lacking the required two, 8 foot ground rods. There is only one ground rod, and it appears to have been installed as a ground for the telephone system. At this point I'm thinking the corrosion and deterioration was not caused by excessive current flowing top ground via this water supply line.

Dave Baylor
- Pittsburgh, Pennsylvania

May 22, 2009

Q. Hi, Our house is 6 years old and from the time we moved in we have had this "green" problem. It has ruined my hair and has left stains in the sinks and toilets. We have had 2 different water softeners and 2 water heaters. We discussed this with the last water softener person and I guess they didn't have a clue about this problem. No one has until I
talked to some nerd at the company that tests the water for the city. He said that it was probably because of the fittings that the water softener company put on the copper pipes and if we didn't rectify the problem, we would eventually have pin size holes in the pipes and leaks! What do we do, who do we call and how do we go about fixing this problem! I want long hair again! Thanks!

Kathy L. Maxwell
- Grover Beach, California

December 8, 2009

A. While replacing the copper piping in a 150 year old home, I was puzzled by the green buildup inside of the pipe. Tracing the pipe I discovered that a ground clamp and wire from the circuit breaker box was connected to the cold water line 15' from the water meter where a jumper wire was also connected to the pipe from the street. In the circuit breaker box the Neutral buss was bonded to the Ground buss. That was okay. I also checked the sub panel to make sure the Ground buss and Neutral buss were not connected.

The wire mains from the electrical meter are aluminum. Current will find the least path of resistance, therefore current leakage to the piping is occurring. The remedy for this is to drive a conductive rod into the ground as deep as local code requires and connect a ground wire. Additionally I moved the ground clamp to the incoming side of the water meter, and removed the grounding jumper. As the water meter has dielectric connections the leakage can not return into the water piping since it is no longer grounded.

Bert Cooper
Equipment Designer - Williamsport, Pennsylvania

June 11, 2010

Q. Type K soft copper pinholes. We are having numerous issues with 3/4" and 1" and even a couple 2" services running from the mainline in the street to the property. 10 years ago or so we started having pinhole leaks appear on the copper always next to a flaired fitting so naturally everyone blamed it on a bad flair, then the specs changed and we were allowed to use compression fittings. This is now happening with the compression fittings as well, now everyone is blaming it on not de-burring the copper properly.

We just had to dig up a leak and found the pinhole leak in the middle of the 1" copper run (no fittings even close) and the copper was in a 4" sleeve under a major street which would eliminate the corrosive soil theory which the supplier will want to use, also the leak was on the top of the copper so a rubbing situation is not the answer. I have a question, is it possible for the copper at the time of production to have impurities introduced causing an electrolysis situation? Do you know of any other town having this problem. The suppliers here have no idea and have never even heard of this problem before which I find hard to believe. Thank you for your time and opinion

Bill Williams
water company - Tucson, Arizona

September 9, 2010

Q. I have recently installed and new water softener with an aerater in my home. My home is 26 years old and several weeks after the installation I noticed a blueish/green tint. I have had the water tested and the copper level is high, can the new system cause this?

Rachele Cancia
home owner - Sunrise, Florida

November 26, 2010

Q. I had an odd situation and was wondering if there is a known reason.
Last evening we noticed water dripping from the ceiling. Upon cutting open the ceiling, I noticed that the 3/4 hot water heating pipe (not sure if supply or return) was pressing firmly against the 1/2 hot water supply pipe, and that a leak had developed in the (smaller) hot water pipe where they touched. Fortunately, the heating pipe was connected to flexible copper to go up through the floor, and I was able to push the pipes apart and repair the supply line easily, but I am concerned what might have caused this leak.

Mike Paulson
former kitchen contractor, retired - falls church, Virginia

December 17, 2010

Below is an excerpt from Wikipedia's "Tap Water" page at

"Pin-hole leaks can occur anytime copper piping is improperly grounded and/or bonded; nonmetal piping, such as Pex or PVC, does not suffer from this problem. The phenomenon is known technically as stray current corrosion or electrolytic pitting. Pin-holing due to poor grounding or poor bonding occurs typically in homes where the original plumbing has been modified; homeowners may find a new plastic water filtration device or plastic repair union has interrupted the water pipe's electrical continuity to ground when they start seeing pinhole water leaks after a recent install. Damage occurs rapidly, usually being seen about six months after the ground interruption."

Q. So if I understand this correctly, adding a union may cause this problem? How does one connect copper pipe to galvanized steel then, or how to bond from copper pipe (cold water line, for example) to iron pipe (gas line, for example)? What materials is the bond conductor made of?

Andy Roberts
- Maynard, Massachusetts

May 13, 2011

A. I have seen electrolysis occur with galv. steel straps, hangers and supports, with copper. It usually occurs at the point.
Pin Hole leaks are mostly caused by incorrect installation of plumbing pipes.
For example, If a plumber uses a pipe cutter, to cut a pipe, it leaves a ridge on the inside of the pipe. This causes a ripple in the flow of water going through the pipe, and will eventually start eating away at the pipe, from the inside out. This was a common occurrence back when track homes were booming, and the track rats were doing high volume production, and not installing correctly.
You can verify this, by separating the pipes at the soldered joint, and stick you finger in the pipe and feel the edge. If you feel a sharp edge, then the fitter never filed the inside edge to remove this. Which this is why it will happen in multiple places in your home. Also the reason it happens more to cold water lines, is because you use your cold water more that your hot.

Keith Van Aalst

- Anaheim California

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