Blue-Green Stains in Sinks and Tubs: What They Mean (Copper + Low pH)

A caller in New York put it the way most people do: "I'm tired of cleaning the green little streaks that are starting to show up on my tubs." His pH was 5.65, and the pinhole leaks had already started. This page is the answer I give on the phone: what the blue-green stain is, how to tell it from the other stains, what your copper number means for your health and your pipes, how to clean what is there, and the one thing that stops it coming back.

What Blue-Green Stains Actually Are

The blue, green, or turquoise ring in your toilet bowl, the streaks below a dripping faucet, and the tint in your tub are all the same thing: copper oxide. Your water is carrying dissolved copper. When that water sits on porcelain, ceramic or fiberglass and evaporates, the copper stays behind and oxidizes into a blue-green deposit. As I say in the video below, there is nothing in the water that is blue until the water passes through your copper pipes. That blue-green color is dissolved copper, and it means your water is acidic and is eating your copper pipes from the inside.

So the copper is not coming from the well. It comes off your own pipes, fittings and brass fixtures (brass is a copper and zinc alloy) when the water is acidic. A house plumbed in PEX on the same water shows no blue at all, because there is no copper for the water to take; the water is not fine there, the warning light is just missing.

Three and a half minutes on camera: why the stains come back after every cleaning, why a softener or whole-house filter will not stop them, and how the calcite tank works.

Is it this stain? Blue-green vs the other colors

The color and the place tell you the cause, and only one combination is copper from your pipes: blue-green where water sits and dries. The table sorts the rest: orange, white, pink, blue in the bowl only, and blue-green on the outside of a pipe each mean something different. The first thing I ask every caller who mentions stains is whether there is any reddish orange with the blue-green. A New York caller at pH just over 6 told me no, "I see bluish green kind of thing"; a Pennsylvania caller at pH 5.9 said the same, "we don't get reddish brown stains, we get blue stains." Blue-green without orange means acidic water and little iron. Both colors together means low pH and iron, and I treat both.

Example	What you see	What it is	What to do
	Blue, green or turquoise where water sits and dries (tub ring, under a drip, the toilet water line)	Copper from your own pipes, dissolved by acidic water	Test pH and copper; pH below 7.0 confirms it. Fix: an acid neutralizer (this page)
	Orange or rust brown, worst in the toilet you use most and the laundry	Iron in the well water (stains from about 0.3 ppm)	The well water test reports the iron number; the fix is an iron filter, not a neutralizer
	White, chalky crust on faucets and shower glass	Hardness (calcium and magnesium scale)	The same well water test reports hardness; the fix is a water softener
	Pink film in the bowl, shower corners, the pet bowl	A bacterium that lives in the air (Serratia) and grows on damp surfaces; it is not in your water	Clean with a bleach-based product. No treatment system
	Blue in the toilet bowl only; sinks and tub are clean	Dye from in-tank cleaning tablets	Stop the tablets. Nothing to treat
	Blue-green crust on the outside of a copper pipe	A wet pipe: summer condensation, a weeping joint, or two metals meeting at one fitting	Insulate or dehumidify, fix the leak, or separate the metals; see blue-green on the outside of the pipe

The last row is the one people mix up with this page. Stains in the tub mean the problem is inside the water. Film on the outside of a basement pipe in July means the problem is basement humidity. Only the first row is treated with a neutralizer.

Certified lab test, $199

Confirm it is this stain: test pH and copper

One certified lab test, mailed to you, run by an accredited lab, gives you the pH that explains the stain, the copper and lead at your tap, and the hardness and iron that decide what else goes in the line.

Get the certified well water test

53 contaminants. Results reviewed by Aidan, in plain English. On city water, use the city water test.

Why it happens: acidic water plus copper pipes

Corrosion starts slowly at pH 6.9 and gets more intense the further the pH drops toward zero. Well water is acidic when the rock it came through had nothing soft in it to neutralize the rain that fed it; where the rock is limestone or iron-bearing, the water picks those up instead and comes up hard, or with iron, or both. The full explanation, and why a neighbor's test tells you little, is on how to fix acidic well water.

It is common. Of 347 certified lab reports from the well water test kits people buy through us, 17 percent came back below pH 7.0. A Delaware homeowner who had just moved into a well house with no treatment wrote to me about blue stains in the sinks and toilet, and I gave him the one-line answer I give everyone: blue-green stains are a sign of dissolved copper in the water from corrosion of copper plumbing due to acid water, and it is a common problem.

What your copper number means

The EPA's health line for copper is 1.3 ppm; staining and a metallic taste start lower, around the EPA's 1.0 ppm nuisance guideline, and the deposit builds wherever water dries even below that. A lab report gives copper in mg/L, which is the same as ppm.

Our own lab data shows how closely copper follows pH. In 312 certified tests with both numbers, about one test in six below pH 7 had copper over 1.3 ppm; at pH 7 and above, about one in a hundred. Lead follows the same pattern, which is the next section.

One thing to know when you sample: water that sat in the pipes overnight (a "first draw") carries whatever the pipes put into it; water taken after the tap has run a few minutes shows what the well itself is doing. I told an Ohio caller in a hundred-year-old copper house to send the lab a flushed sample to learn about the well. If you want to know what your family drinks at breakfast, take the first draw; one customer's kit read lead at 0.002 ppm first thing and below 0.001 after a three-minute flush. A blue-green stain means the first-draw number is the one worth knowing.

Is copper in the water dangerous?

The stain is harmless; the copper is a health concern only above the EPA action level of 1.3 ppm, and of the acidic wells my customers have tested, about five in six come in below it. Above the action level the EPA lists gastrointestinal distress from short-term exposure, liver or kidney damage from long-term exposure, and advises people with Wilson's disease to consult their doctor if the copper in their water exceeds the action level.

The bigger health question hides behind the copper. If the house was built up to 1986 (or a few years after), the copper joints were made with lead solder. The same acidic water that leaches copper leaches lead, and the EPA's action level for lead is 0.015 ppm. In the tests my customers have sent in, lead over that level showed up in about one test in seven below pH 7 and 8 percent at 7 and above. Raising the pH to 7 or above stops the corrosion, which is what stops lead getting into the water. A blue-green stain in a pre-1986 house is the reason to test for lead in the same sample as the copper and pH. Whether acidic water itself is a health problem is a separate question, answered on are you drinking acidic water.

The stain is the warning; pinhole leaks come next

Blue-green stains and pinhole leaks in copper pipe are one problem, not two: every bit of copper on the tub came out of a pipe wall. The caller in the opening had both: "we're getting pinhole leaks," and he wished he had smartened up a few years earlier when the water was tested at purchase. What I told him is that a home-sale water test only checks that the water is potable and tests for bacteria; nobody looks at pH. Another buyer, two years into a house whose pH turned out a full point low, found a stainless steel pump corroding and copper so thin he could not understand it when he re-plumbed.

How fast it goes from stain to leak depends on the pH and the pipe, and that timeline has its own page: how long acidic water takes to damage a house. The repair side, including what to do about a leak that has already started, is on pinhole leaks in copper pipes. The short version is that a neutralizer stops new metal coming off the pipe, and metal that is already gone does not grow back, so the earlier the pH is fixed the more pipe you keep.

Removing the stains you already have

Copper stains come off porcelain with a mild acid and a gentle abrasive, and they come back within days if the water has not changed. The usual method, and the one the top answers online agree on: white vinegar with salt or baking soda worked into a paste, left on the stain, then scrubbed with a non-abrasive sponge and rinsed. I put it plainly in the video: if you are getting blue-green stains and today is Monday and you clean them off, they are going to be back by Friday. Clean once after the pH is corrected, and you are done cleaning them.

The permanent fix: raise the pH so the water stops dissolving the pipe

A calcite acid neutralizer installed after the pressure tank raises the pH to about 7, and at 7 the water stops taking copper off the pipe; that is what ends the staining. It is a tank of crushed limestone. Water comes in at the valve, travels down the center tube, spreads out through the plate at the bottom and rises up through the calcite, dissolving a little of it on the way and coming out neutral. Nothing is injected and the non-backwashing model does not plug in. When a caller with a strip reading between pH 4 and 5 asked what he needed, I told him a 2.5 cubic foot non-backwashing neutralizer with calcite and FloMag mixed in, which would put his pH between 7 and 8 during water use so there would be no more corrosion of the copper plumbing and the blue-green stains would be eliminated.

Two things a neutralizer is not. It is not a softener or a whole-house filter: people ask me whether one of those will solve the stains and I tell them no, because neither changes the pH, and the pH is the problem. And it does not remove iron, so if you have orange stains too, the iron gets its own filter after the neutralizer. What goes in the tank depends on your pH: plain calcite handles pH 5.5 and above in a 2.5 cubic foot tank, and below that FloMag (magnesium oxide) is mixed in with the calcite; I gave the pH 4 to 5 caller 3 to 4 pounds of FloMag per 50 lb bag. Which size and which mix your numbers call for is the buying table on how to fix acidic well water, with the household-size detail on the sizing guide; the 2.5 cubic foot tank in the photo is $1,495 shipped with five bags of calcite, and every model is on the acid neutralizer collection page.

Maintenance is one job: on a 2.5 cubic foot tank you add one 50 lb bag of calcite about every 24 to 36 months, whether the house has two people or six. The tank is translucent enough that a flashlight behind it shows the level. That, and a sediment filter ahead of the tank to keep dirt off the calcite, is the whole routine; the step-by-step is on servicing your acid neutralizer.

Ask Aidan

Have a pH or a copper number and want to know what it means?

Text me a photo of the report, or just the pH. I'll tell you whether the stains are acidic water, which tank fixes it, and whether anything else belongs in the line.

Text Aidan 443-277-2204 Call800-460-5810Aidan

8 AM to 5 PM Eastern, seven days a week. A real person, usually Aidan.

What buyers saw after the neutralizer went in

Six verified buyers who bought a neutralizer for blue stains or copper wrote back that the blue stopped; the two who retested copper saw it fall from 2.3 ppm to under 0.5, and from "an unhealthy level" to well below the threshold for concern. We searched every review on our product pages for "blue", "copper" and "stain"; these six are all of them, in the buyers' own words, and none reported that the blue kept coming.

Two of them said something worth knowing before you buy. Frank M. noticed a white film in his stainless pans after filling the tank; that is calcite dust from the fill and it rinses out, which is why one reviewer plumbed a hose bib after the tank to flush it on startup. And Richard P., buying replacement calcite years later, wrote that we walked him through mixing calcite and Corosex to reach a pH that would stop harming his copper. The mix is set by your pH, and it is a phone call, not a guess.

Blue-green stains on city water

If you are on city water and your pH tests near 7, the copper is coming from somewhere other than acidic water, and a neutralizer is not the fix. A caller in Georgia had exactly that: an apartment on city water, pH 7.0, a lab test high in copper, the worst stains in the bathtub and a blue stain forming at the top of her Brita pitcher. I told her the copper could be coming from somewhere else in the lines, and that on city water the thing that takes copper out of drinking water is an under-sink reverse osmosis system; a Brita or other carbon filter typically does not remove it. Utilities are required by the Lead and Copper Rule to control corrosion when customer taps exceed the action level, so a high copper reading on city water is also worth reporting to your water company.

For the drinking tap, our reverse osmosis systems start at $275. For the stains themselves on city water there is no whole-house tank to sell you; the copper is not coming off your pipes because of pH, so my honest advice is the city water test first, then a call about what the numbers show.

Frequently Asked Questions