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Copper staining from hot water?

dm9321287
dm9321287 Member Posts: 31
edited April 15 in Domestic Hot Water
I'm wondering if anyone has any ideas what might be causing our domestic hot water to leave blue staining in the sinks/showers?

I understand the blue is copper, and from what I've learned, that's most often caused by either acidic water or bad electrical grounding. I've home tested the water acidity and it's normal, and nothing has changed with the electrical grounding to the mains stop tap under the kitchen sink.

We did have a mains supply pipe leak last year we were unaware of until the massive bill arrived from the supplier, and the blue water started to appear during this time. We've had the pipe replaced with a new plastic pipe, but the blue water continues.

I'm wondering if the water supply might have become contaminated during that time, tipping it slightly to the acidic end, and that's found its way into the copper DHW storage tank?

What's confusing me though, is why is it persisting, if the water is not acidic and the grounding appears to be fine. Could it be that the storage tank is just past its sell by date and slowly corroding? That said, we had it put in when we bought the house about 13 years ago. Is that about right for replacement? Or maybe it's not likely to be the tank at all?

Grateful for any thoughts.

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 15,842
    The copper staining which you describe is almost always -- not quite, but almost -- because the water is slightly acidic. It doesn't take that much, particularly if the water is also relatively sot.

    So... you describe the pH as "normal" -- but that can be anywhere from 5.5 up to almost 8. What is it? And is the water relatively soft? Or more particularly, softened?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Larry Weingarten
  • dm9321287
    dm9321287 Member Posts: 31
    @Jamie Hall , thanks for the very prompt response. You'll have guessed I said 'normal' because I couldn't remember exactly, but the ph was what it was supposed to be according to the supplier. I'm going to guess 7 but could always easily check again.

    We live in an extremely hard water area and have used the same softener since the day we moved in. So yes, that could well be putting the water on the soft side, but why would the corrosion have become more noticeable now, unless of course, it's been happening all this time and only now become noticeable?
  • Jamie Hall
    Jamie Hall Member Posts: 15,842
    The combination of slightly acidic water and ion exchange water softening can produce copper staining -- as to why it might have changed recently, haven't a clue. Sorry...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Larry Weingarten
    Larry Weingarten Member Posts: 2,147
    Hi, Softening can cause this problem if it’s overdone. You should leave 60-120 ppm of hardness in the water.

    Yours, Larry
  • ratio
    ratio Member Posts: 2,764
    If you went from a metallic service line to plastic, it may be that the bonding isn't as good as you suppose. Even a rusty pipe in the ground is a better grounding electrode than a plastic pipe.
    Canuckerbburdmattmia2
  • dm9321287
    dm9321287 Member Posts: 31
    ok, thanks everyone for your input. I am very likely going beyond my very limited expertise here, I thought the water feed was bonded to protect against the pipework being charged, as opposed to providing the earth itself?

    Here in the UK, replacement of water feeds with plastic piping is now standard practice, as the old iron (or worse, lead) pipework put in over a century ago all disintegrates. The bond is to the copper next to the stop tap where the supply enters the kitchen. The mains gas pipe is similarly bonded before it reaches the meter. Both of these earth cables return back to the consumer unit.

    I'd have thought, but could very well be wrong, that even if the water supply pipe is no longer providing adequate earthing itself, the fact it's connected back to the gas pipe (via the consumer unit), would still provide good grounding (assuming there's not another grounding to the consumer unit, which I'm guessing there probably is)?

    All that said, the problem started before the water pipe was replaced and the supply was bonded in exactly the same way (albeit the feed pipe was metal). So is it not most likely something else?

    Noting the comments about the softener, and having retested the water last evening (it's coming up between 7 and 8 ph, so slightly alkaline, if anything), I am completely perplexed. Something is obviously causing copper corrosion in the system, and most likely in the hot water storage tank, given the blue is coming from the hot water (I understand the corrosion is exacerbated when the water is heated).

    The softening level of the softener cannot be adjusted. The whole thing is entirely automatic, and operates kinetically. You put in blocks, it softens as needed. Been doing that for 13 years here, and 4 years in pervious house. Granted, it could be knackered, but I wouldn't say the water is noticeably soft, just not hard.

    I guess one option would be to bypass the softener for a while and let the water harden, so as to see what happens? Would this cause the staining to stop notwithstanding any legacy corrosion within the tank? It would certainly identify the problem if it's the softener.

    Alternatively, would it perhaps be worth trying draining down the hot tank completely and seeing if that removes any corroded sediment that may have occurred through mineral ingress when the supply pipe was failing last year? Or would that more likely make things worse?

    If need be, I'll just swap the tank out (and will discuss with my engineer when he visits again in the next couple of months to service the boiler), but I'd ideally like to get a clearer idea as to whether that's necessary before I go there, or if there might be a simple fix somewhere that could correct this.

    Could it be, for example, as simple as an electrical cable in close proximity to water pipes? We have a lot going on in the system in a couple of places (powering controls and pumps, for example), and whilst all the cables are correctly insulated, is there any way they could be charging the copper pipework somewhere?

    Or is it just that some of the pipework in this old (125 year plus) house is likely knackered?

    Further thoughts very much appreciated.
  • Larry Weingarten
    Larry Weingarten Member Posts: 2,147
    "I guess one option would be to bypass the softener for a while and let the water harden, so as to see what happens? Would this cause the staining to stop notwithstanding any legacy corrosion within the tank? It would certainly identify the problem if it's the softener." YES!

    Yours, Larry
  • ratio
    ratio Member Posts: 2,764
    Check for bonding jumpers around the water heater & softener, from inlet to outlet. I'm unfamiliar with your style of appliances, but over here a water softener may very well be 100% plastic. if the inlet was 'bonded' via the old water service line, it could be floating now.
  • dm9321287
    dm9321287 Member Posts: 31
    edited April 17
    Thanks again @Larry Weingarten and @ratio for your further input.

    I've taken a closer look at the bonding and I think if anything, that might be the cause. The plastic water mains supply pipe connects to copper, which is bonded. That then connects to plastic and goes off to the softener where it connects to copper, goes through the plastic softener, connects again to copper, then plastic again to come and back to the original copper before going off into the rest of the house.

    I'm wondering therefore, whether the plastic possibly creates the 'floating' bond, i.e. only the kitchen sink (unsoftened) water tap is bonded, and once it connects to the plastic to go to the softener, the earth is lost. That said, when it comes back and connects to the copper to go to the rest of the house, a small run of that copper is in the concrete slab in the kitchen floor, before it goes off under the suspended floors. Could that immersion in the concrete slab be sufficient to earth it from that point on? I'm wondering if that's why it's not re-bonded.

    If the concrete is an insufficient earth, I'm guessing I can bond by connecting the current bonded point to the exiting copper pipework that runs off into the house (bearing in mind that the only accessible pipework I can connect to is the feed to the dishwasher, which tees off from the pipework that runs through the concrete slab)?

    Am I thinking along the right lines here? Thanks again.
  • ratio
    ratio Member Posts: 2,764
    I would think embedded in concrete sufficient grounding to prevent issues, but it likely doesn't meet the code definition of bonding. I'm not familiar with your codes, but over here I'd throw a bonding jumper across every discontinuity in the metallic piping, & verify there's a properly sized jumper in place to the grounding electrode.

    These names are from the National Electric Code & might not line up with the definitions in whatever code you must follow, but the concept should be the same.

    I'm basing all of this on the fact that it started immediately after the old pipe was replaced with non-metallic.

  • dm9321287
    dm9321287 Member Posts: 31
    edited April 17
    Thanks @ratio, very helpful, once again.

    Technically, I believe the pipework is bonded compliant with the UK regs, at least insofar as there is main bonding from the central grounding to the copper pipework immediately after the plastic supply pipe. It was connected here before the supply pipe replacement.

    The staining didn't start after the pipe was replaced. It's been noticeable for some time now, and I thought it might perhaps be linked to the degrading metal supply pipe (once I learned of the leak). In other words, was the degradation of the metal supply pipe somehow increasing the acidity of the water? It seems not, as changing the pipe has done nothing for the staining (but has drastically reduced our water bill).

    Having tested the water myself (not professionally), I don't believe it's acidic, either at the mains or after the softener. Therefore, it must be something else and the only other cause I'm aware of is faulty bonding.

    Given it's apparently compliant with the regs (main bonded and grounded), the only thing I can think is that the bond is lost somewhere after the bonding. The would most obviously appear to be when the pipework switches to plastic to go off to the softener, before switching back to copper after the softener. That subsequent copper work is not therefore bonded (loss of continuity) but as I mentioned, it is initially set in concrete. After that point, I believe it's copper throughout, and importantly, all the way to the indirect hot water cylinder.

    I guess at the end of the day, it's probably a process of elimination, and connecting a bonding jumper from the currently bonded point to the pipework after the softener is easy enough to do and may well solve the problem (unless of course the concrete slab negates the need to do that). If it doesn't, then I am well and truly stumped.

    Thanks again for your help. As I've always found on here, experienced input triggers thought processes that can often take one down the path to a possible solution.
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