Copper water supply pipe corrosion & leak © Daniel FriedmanAcidic Corrosive Water
Detection, effects, cures for low pH aggressive water. Langlier Index

  • CORROSIVITY or ACIDITY of WATER - CONTENTS: what are the effects of low pH, acidic or corrosive water on building piping, leaks, dissolved copper, health hazards, and the plumbing system in general? How do we detect corrosive or aggressive water and what should be done about it.
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Aggressive, corrosive, low pH water - acidic water:

This article describes effects of low pH, acidic or corrosive water on building piping, leaks, dissolved copper, health hazards, and the plumbing system in general? We describe how to detect corrosive or aggressive water and what should be done about it.

The Langlier index is defined and its use in evaluating the corrosivity of a water supply is explained. This article also describes other factors in the formation of leaks in building water piping including scouring, debris, & the effects of hot water on water pH. The article links to more information about green stains traced to the water supply.

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Acidic water & copper pipe corrosion/leak risk / leak prevention

pH scale for common materials  - water: At "COPPER PIPE PINHOLE LEAKS: cause, cure, prevention" we point out that water chemistry itself can be a source of metal water pipe (and even drain pipe) corrosion. From Environment-Canada [at left] you can see a pH scale showing that high pH numbers are acidic while low pH numbers mean that a substance (water in our case) is basic.

[Click to enlarge any image]

Neutral pH values are in the middle of the range. Low pH or acidic water is corrosive or is referred to as aggreesive water. Before we explain the details of the causes and effects of aggressive or corrosive water, here is an except from our copper pipe leak discussion:

If the pH is low <6.0, the hardness low generally<50ppm, the alkalinity low generally <40ppm, the water could be considered extremely “soft” and aggressive to the home’s metallic plumbing system.

If the chlorides are elevated >100ppm this would only compound the problem. The water should be treated to make the water less aggressive by raising the pH, alkalinity or hardness. - CT DOH.[1]

Reader question: Sage advice needed about corrosive / acidic well water

I have fairly acidic well water on Cape Cod – pH 6.3. I get a lot of blue stains on bathtubs and sinks, which I assume is copper leached from the inside of the copper water-supply piping. I built the house about 16 years ago and replaced the water heater a few years ago.

Am I at risk of developing pin holes or other damage to the copper plumbing and other equipment, including an electric water heater, boiler, and baseboard radiation?

If that’s the case, what’s the preferred (and cheapest) solution: calcite neutralizer tank, soda ash feeder, or other?

FYI, copper level was last measured at 0.11 mg/L, well below the MCL of 1.3, so I don’t think there’s a health issue. But I figure if copper gets leached from the pipes for enough years, at some point there won’t be much pipe left.

Muchas gracias, Steven Bliss, 4 Burlington, VT


I do not have experience with pH treatment first hand, but it appears to me that the short answer is that for most situations, calcite filters are the easiest and cheapest method of treatment. But certainly experts have been looking at this problem for along time, and continue to research it. See Mattsson et als [14][15].

Before choosing one I'd measure the Langlier Saturation Index (LSI) of the water so you can figure out the level of treatment needed and check that against the treatment method proposed.

Incidentally, before water testing or asking your test company about what they commonly find in wells in your area of Cape Cod, don't rule out the water supply itself as contributing to the supply of dissolved copper. You could easily distinguish between copper from acidic effects on copper water piping and copper in the water supply by comparing two water tests, one taken from in the building (I give some aggressive testing suggestions below) and one taken from water where it enters the building, presumably through a plastic or galvanized iron well pipe (not a copper one).

Until you know the score, if there is a worry that pipes may already be thin or at risk, that's an extra reason to shut off water when leaving the property unattended. Some of the suggestions

Water conditions causing pitting and leaks in copper piping

Mattsson et als (1968) provide a helpful elaboration of the causes of failures in copper piping due to pitting and corrosion from which we quote these excerpts:

An investigation of failures of hard-drawn copper water pipes (phosphorus-deoxidised copper) in service due to pitting corrosion was conducted from November, 1962 to February, 1965. Fifteen cases were reported. All those about which information could be obtained came from hot water installations and occurred in water with a low pH (?7) and a HCO3- content of, at the most, 100 mg/l but generally below 50 mg/1. Failures not due to pitting corrosion (i.e. caused by erosion and corrosion or corrosion fatigue) occurred in waters with a higher pH and higher HCO3- content.

A laboratory investigation into the ability of the corrosion products to counteract further corrosion in different types of water was also carried out, using an electrolytic cell which, in principle, was a model of an active pit in a copper tube. This led to the following conclusions, which are in good agreement with the results obtained from the examination of service failures:

If the pH value of the water is high enough, the copper dissolved by the corrosion can be precipitated as basic copper salt. At low pH values such precipitation does not take place.

If the [HCO3?]/[SO42?] ratio in the water is high, dissolved copper can be precipitated as basic copper carbonate in the neighbourhood of the corrosion site and counteract further corrosion.

At a low [HCO3?]/[SO42?] ratio, crusts of basic copper sulphate will be precipitated at some distance from the corrosion site and may lead to a high corrosion rate.

Pitting is not likely to occur in hot water tubes of hard copper if the pH is ? 7·4 and the [HCO3?]/[SO42?] ratio ?1 (the concentrations given in mg/1). The critical values mentioned are approximate and may be adjusted in the light of future experience. - [14] "Pitting Corrosion in Copper Tubes – Cause of Corrosion and Counter-Measures", Mattsson, E.; Fredriksson, A.-M., British Corrosion Journal, Volume 3, Number 5, September 1968

Health and aesthetic impacts of copper corrosion on drinking water

Traditional research has focused on the visible effects of corrosion--failures, leaks, and financial debits--and often overlooked the more hidden health and aesthetic aspects. Clearly, corrosion of copper pipe can lead to levels of copper in the drinking water that exceed health guidelines and cause bitter or metallic tasting water.

Because water will continue to be conveyed to consumers worldwide through metal pipes, the water industry has to consider both the effects of water quality on corrosion and the effects of corrosion on water quality. Integrating four key factors--chemical/biological causes, economics, health and aesthetics--is critical for managing the distribution system to produce safe water that consumers will use with confidence.

As technological developments improve copper pipes to minimize scaling and corrosion, it is essential to consider the health and aesthetic effects on an equal plane with chemical/biological causes and economics to produce water that is acceptable for public consumption. - [15] "Health and aesthetic impacts of copper corrosion on drinking water", Dietrich AM, Glindemann D, Pizarro F, Gidi V, Olivares M, Araya M, Camper A, Duncan S, Dwyer S, Whelton AJ, Younos T, Subramanian S, Burlingame GA, Khiari D, Edwards M., Virginia Tech, Blacksburg, VA 24061-0246, USA., Water Sci Technol. 2004

Acidic Water Treatments to Raise the pH: Calcite Filters vs. Soda Ash Injection

According to the Clean Water Systems & Stores (who sell this equipment) , calcite neutralizer filters

... will typically raise the pH of the water to 7.0 to 8.0 and add 30 to 100 ppm of hardness depending on the alkalinity and water hardness. [2]

More sophisticated is a soda ash injection system. That approach requires a pump and metering device along with an intermediate tank to give the water enough contact time with the soda ash. And room to store 25 or 50 pound bags of soda ash. Like some other water treatment systems (like a chlorine injector) the soda ash injector pump is hooked up to run when the well pump turns on. It seems that a soda-ash injector system is recommended when the low pH of water is due to dissolved mineral acids (do you live near a mining site or in New York a natural gas from shale mining operation?).

Chemical Feed / Neutralization Soda Ash: water treatment systems dispensing a soda ash chemical feed are used to correct high water pH (acidic) conditions by injecting a base (soda ash) into the water supply followeed by filtration. Water high in natural acids or high in carbon dioxide (CO2) are acidic and are likely to need a treatment of this type.

Definition of the Langelier Saturation Index - LSI & How it is Used

On acidic well water and water corrosivity - using the Lange Saturation Index

Deposits and stains on faucet strainer (C) D FriedmanIt's true that the lower the pH (more acidic) the higher the level of corrosivity of the water supply.

But because pH is only one of several factors that will determine how corrosive the water is, while we should look at acidity or pH, if you want to know how worried to be about your water supply corroding your pipes, you want to perform a corrosivity test on your water.

But looking at building water supply properties and pipes and fixtures for evidence of what contaminants or water chemistry problems may be present can be confusing.

Our faucet outlet (photo at left) shows both thick white mineral deposits (suggesting high calcium and high pH) and blue/green stains and deposits that might to some suggest acidic water and low pH.

While there is no doubt your water is acidic, there are other factors affecting corrosion of piping. Let's start by looking at the LSI.

Experts us the Langelier Saturation Index (LSI) to estimate the corrosivity of a water supply. The Langelier Saturation Index or LIS is a number calculated from several factors and intended to tell you the chances that minerals, principally calcium are likely to precipitate out of the water.

Langelier, who developed this index, realized that the acidity or pH of water determines how much calcium carbonate CACO3 the water can hold. So a combination of the water's actual pH and the actual level of calcium in the water, along with other factors we list below, allow us to predict the chances that the water will leave scale in the plumbing system or components by precipitating out the calcium. We think of it as a more complete picture of water chemistry, with regards to both hardness (mineral content) and acidity or pH.

The Langelier calculation factors in the main components of corrosivity of a water supply including:

  • Temperature of the water
  • pH of the water
  • total dissolved solids or TDS in mg/L
  • Calcium level Ca in mg/L and whether or not the Ca is in the form of calcium carbonate CaCO3 or calcium ions Ca2+
  • Alkalinity of the water (in mg/L as calcium carbonate) these produce a Langelier Saturation Index.

Action Levels in the Langelier (LSI) Index

Mineral scale CaCO3 formation on a water supply pipe (C) Daniel Friedman illustrating Langlier Index Scale FormationThe Langelier index, when calculated ranges from +4 through 0 to -5. But you don't have to calculate anything. Just ask your water test company to perform this test for you, OR ask the water test company to test your water for hardness (you can do this free or cheap
at MEASURE WATER HARDNESS ) and for corrosivity.

+4 LSI = scale producing water: At +4 the water is very likely to form scale or typically calcium carbonate (CaCO3) and magnesium deposits in the water piping, especially hot water piping or in a water heater.

Readers whose water is hard and/or has a high positive Langelier index should
see WATER SOFTENERS & CONDITIONERS. More generally, a Langelier saturation index or LSI greater than zero means that the water is super saturated with minerals and therefore will tend to precipitate mineral deposits or form scale in building piping, fixture, and the water heater or geyser or water cylinder.

Zero LSI = just right: like the baby bear who found one of the porridges "just right", At an LSI of zero the water supply is "neutral" - it is not likely to precipitate calcium into the piping nor is it acidic enough to dissolve more calcium. With respect to the corrosive effects of acidic water on copper water piping, an LSI of zero also means the water is close to ideal - it is not corrosive to the piping.

More generally, LSI=0 means that water is saturated but not super-saturated with minerals. The water is "neutral" and will neither deposit scale nor dissolve solid minerals such as CaCO3.

At -5 LSI = corrosive water: at -5 LSI the water is extremely corrosive. Langelier index values of +0.5 to -0.5 are basically OK in that you wouldn't treat water at those levels.

More generally, at an LSI less than zero water is "under-saturated" with minerals and thus is likely to dissolve CaCO3 as well as possibly metal piping or other materials. This is an "aggressive" or acidic water supply.

If you decide to treat the water based on acidity alone or based on a Langelier index reading of -3 or lower (or optionally anywhere below -0.5) there are various systems that inject something basic like calcite (a calcite neutralizer tank or calcite neutralizer filter) or soda ash (a soda ash feeder) to treat the water and described above.

Other Indexes of Water Condition: Ryznar Stability Index, Puckorius Scaling Index, Stiff-Davis Index, Oddo-Tomson Index

Other indices of water condition include the Ryznar Stability index that predicts water chemistry and how it will affect piping and appliances by examining the thickness of scale formation in municipal water systems, the Puckorius scaling index, the Larson-Skold index, the Stiff-Davis Index, and the Oddo-Tomson Index.[4]

The Ryznar Stability Index (RSI) was developed from actual observations of steel water main pipe corrosion and scale deposition.

RSI = 2 pHs - pH

where the pH is measured. An RSI between 6 and 7 is at "saturation equilibrium" and thus is similarly neutral as a 0 LSI index reading. At RSI greater than 8 water tends to be corrosive or to dissolve CaCO3. For an RSI below 6,5 water tends to deposit CaCO3 or to form scale.

Inspect your copper piping for evidence of leaks, corrosion, pinholes & leak risk factors

First, what quality of copper has been installed. Copper piping is sold in different weights or thicknesses. M is thin-walled, used in heating baseboards (you should be ok with that as the water in a hot water heating system does not keep changing out so corrosivity is normally limited); Types K (thickest) and L are used for water piping, M being the heavier grade, more resistant to corrosion perforation.

Therefore if your distribution piping is Type L you should inspect for corrosion on the pipe exterior - and beware that a small blue dot, when you scratch it, may become a rapid leak. Don't ever "pick" at corrosion unless you're prepared to shut down the water supply and clean up a leak. The bad news that has come up with some InspectAPedia readers, is that if you discover a length of copper piping with imminent or current pinholes, replacing just that section is not very comforting. Because the piping is corroding from the interior out, you won't see how thin and fragile other piping sections are ... until the next leak.

Also, corrosive water combined with waste and waste water risks corroding copper drain piping. Surprisingly you need to look along low-sloping runs of copper drain piping for evidence of corrosion or leaks along the top of the pipe, not just the bottom. It appears that droplets of highly corrosive condensate form along the upper surface of the pipes and remain in place for long periods, never being washed away by drain usage.

The World Health Organization, WHO Advice on Water pH - health effects

Exposure to extreme pH values results in irritation to the eyes, skin, and mucous membranes. Eye irritation and exacerbation of skin disorders have been associated with pH values greater than 11. In addition, solutions of pH 10–12.5 have been reported to cause hair fibres to swell (10). In sensitive individuals, gastrointestinal irritation may also occur.

Exposure to low pH values can also result in similar effects. Below pH 4, redness and irritation of the eyes have been reported, the severity of which increases with decreasing pH. Below pH 2.5, damage to the epithelium is irreversible and extensive (10). In addition, because pH can affect the degree of corrosion of metals as well as disinfection efficiency, it may have an indirect effect on health.

In addition, if well water at a particular building also happens to require disinfection, the pH is important and needs to be below 8.

What is the Optimum pH for a Building Water Supply?

WHO says in general the optimum pH target for drinking water should be 6.5 - 9.5, adding " No health-based guideline value is proposed for pH." [but they didn't appear to consider the effects of dissolved copper - if it occurs]

Other Causes of Pinhole Leaks in Copper Pipes in Buildings

Copper pipe ground bonding (C) Daniel FriedmanOther causes of copper pipe pinholing or holing and leaks include

  • Galvanic corrosion -
  • Scouring of the pipe interior by unusually high velocity water flow through the system.
  • Sand, silt, or other abrasive contaminants in the water supply (you will probably detect these by clogged strainers at your faucets or clogged shower heads),
  • Improper or missing electrical grounding of the electrical equipment or any other electrical appliances in the building, including the presence of stray voltage in the grounding system or poor bonding of the grounding conductors to metal piping, or its interruption
    by DIELECTRIC FITTINGS or other components. "Bonding" means that the metallic parts are permanently joined to form an electrically conductive path ... to reliably conduct electrical current. "Grounding" refers to the connection of an electrical circuit or component to the earth. - Roberge (1999) & NEC Article 100

    We discuss corrosion due to electrical grounding system errors in more detail
  • Lightning strikes or electrical arcing from nearby electrical components - as I describe just below

We joined in investigating a site that had suffered what appeared to be a lightning strike - it was actually an electrical discharge from a high voltage power transmission line. A tree grew tall enough to contact the line, conducting power to the ground close to the home.

Moisture under the garage floor slab vaporized, exploding the floor, sending the car up through the garage roof.

Electricity traveled across from the garage, apparently following tree roots, up an iron entry stair railing, over to aluminum siding (all the aluminum pop rivets melted and all of the the siding corner trim pieces fell to the ground), around the siding to a metal outdoor hose bib to metal water piping. Inside the building the water pipe was fused and melted, causing a basement flood.

Electrical Ground Wiring Errors Can Cause Plumbing Pipe Leaks

Electrical ground corrosion at water pipe (C) Daniel FriedmanWatch out: also to check for electrical system connections that can significantly increase the risk of corrosion of the copper piping in the building.

As you know, at most buildings the water piping system is grounded for safety, and sometimes a metal well pipe extending outside underground is used as a grounding electrode as well. Electricians recommend two driven grounding electrodes at modern properties (you can leave the old connection to a metal well pipe in place).

But interestingly, a mistake in the electrical panel, for example one that sends current improperly down the ground path, can speed up corrosion of building metal water pipes or other components.

I had a client in Pleasant Valley NY who twice replaced a very costly, supposedly corrosion proof nickel-plated co-axial ground-water-source heat pump temperature exchange coil. The purpose of the coil was to cool high temperature refrigerant gas back to a liquid state by cooling it using water pumped from a nearby well and for efficiency recycled through a holding tank for re-use before it was returned back to the ground from which it had originated.

When the heat pump stopped working I found that all of the refrigerant had leaked out of the system. But I couldn't find a leak in the refrigerant piping system. The only component I could not test directly with my halogen leak detector was the water-to-air heat exchanger coil itself. In an exciting discovery, I opened a drain to release water from the water-to-air heat pump system's water reservoir tank.

When I held my leak detector near the water stream, the detector went crazy, responding to a very high level of refrigerant gas that had become dissolved into the water.

We realized that the heat exchanger coil that was supposed to just cool the refrigerant gas was instead leaking that gas right into the cooling water supply.

Someone smarter than we were figured out where to look. The technician determined out that the heat exchanger coil was corroding and perforating because of improper electrical grounding within the heat pump.

Recommended Maximum Limits for Copper in Drinking Water

EPA's list of limits on contaminants in water ( is set in MCL (Maximum Contaminant Level), MCLG (Maximum Contaminant Level Goal) or mg/L (milligrams per liter) (mg/L === ppm) or parts per million - two ways of describing the same concentration

For copper EPA recommends both a MCLG and an "action level" of 1/3 mg/L for copper in drinking water, citing short term gastrointestinal distress (short term exposure) or liver or kidney damage (long term exposure). EPA also warns " People with Wilson's Disease should consult their personal doctor if the amount of copper in their water exceeds the action level"

Test the level of copper in your water - how to construct a "worst case" test

It would be instructive to test your water's copper content to see if it's unusually high. Not only would that tell us if acidic well water is corroding the pipe interior, you might find that the levels of copper are high enough to merit action for water safety / potability.

Making a "worst case" (most critical or "safest") measurement for copper or any other contaminant that might be found in drinking water due to dissolving the contaminant out of the water piping and supply system equipment can be done following the DF approach. We want to collect a sample of water that is most likely to represent the highest concentration likely to occur in household water that someone might drink.

To construct the "worst plausible case" scenario we collect a water sample after water has been sitting in the pipes for some time period. A longer wait period (days, weeks, months) might represent a house that has sat unoccupied for some time. But in my opinion I'd collect water that has sat overnight as a more likely and thus more plausible "worst case" scenario.

If all of the house plumbing is copper, you would, on "the morning after", go to a plumbing fixture most distant from the incoming water supply, pump, and tank, open a cold (test 1) water faucet and run enough water to flush out the faucet and any plastic fixture risers, so that we're sure we've got water that was in the copper piping overnight. Then collect the sample.

Watch out: at WATER TESTS for CONTAMINANTS we discuss testing well water quality - what is "in" the well water that may make it unsafe or unpalatable to drink. Water that may be too high in mineral content, clogging pipes and water heaters
or water that is too acidic or corrosive, causing leaks in copper piping or that causes green water or stains on plumbing fixtures & laundry

Hot water and water pH - what happens to pH when we heat up the water?

You could collect a hot water sample as well, running water until it's hot, but because the "hot" water has arrived fresh from the water heater tank, it has not sat overnight in the piping and so is not such an aggressive test - I wouldn't bother. Not unless your home uses an antique copper water heater tank.

The WHO guidelines for drinking water quality points out some interesting technical detail,including that (at least for pure water) heating the water will decrease the water's pH. A pH decrease of 0.45 occurs when you raise water temperature by 25 deg. C. [13]

If the house has part plastic water supply piping, you'd want to see where the copper is located, calculate (by linear feet of pipe and its diameter) how much cold to run out to be sure you've collected a sample from inside the copper pipes.

That about exhausts me on copper pipes, pH, corrosion, copper testing, Langelier index, and treatment for low pH water. Thanks for asking.


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