: Water Testing >> Langelier

Langelier Saturation Index

Langelier Saturation Index, or commonly Langelier, or LSI, is based on the investigation of the carbonate equilibrium in water, to assess the true pH or true hardness of water.

The components that make up the carbonate equilibrium are gaseous carbon dioxide CO2, aqueous carbon dioxide (CO2)aq, carbonic acid H2CO3, bicarbonate HCO3-, carbonate CO3/2- and solids containing carbonate like calcium carbonate CaCO3 or magnesium carbonate MgCO3.

More simply, it is a calculation method based on certain water testing parameters that give a more accurate or true investigation as to the corrosivity index or corrosion potential or water aggressiveness or true pH, on one hand, or on the other hand the scaling index, or hardness potential or true hardness, rather than just basic water test figures which may not reveal the full picture of how the water is behaving.


Water is an effective solvent and picks up impurities easily.  Pure water is defined as tasteless, colourless and odourless, with a neutral pH of 7 and is often called the universal solvent.  Dissolved solids refer to any minerals, salts, metals, cations or anions dissolved in water.  Total dissolved solids or TDS, include inorganic salts (mainly calcium, magnesium, potassium, sodium, bicarbonates, chlorides and sulfates) and some small amounts of organic matter that are dissolved in water.

Corrosivity is a measure of how aggressive water is, for example when corroding pipes and fittings.  Corrosive water can leach iron, lead, copper, etc., from pipes into drinking water and can eventually cause leaks in plumbing.

Corrosion in general is a complex interaction between water and metal surfaces and materials in which the water is stored or transported.  The corrosion process is an oxidation / reduction reaction that returns refined or processed metals to their more stable and natural ore state.  With regards to the corrosion potential of your own drinking water, the main concerns are the presence of toxic metals, such as lead and copper and having a bitter or metallic taste in the water, and in relation to the use of corrosive domestic household water through the general plumbing system, the concerns are for pipework, tanks, fittings and bathroom sanitary ware, and with the aesthetic problems of stained laundry and greenish blue stains around basins and drains.

When a household is plumbed using a high level of copper pipework (grade of copper important) and either aggressive langelier (usually less than -0.5) or very high water volumes / fast water flows / high water pressures, are experienced or a combination of these and other adverse physio-chemical conditions that can lead to copper oxidation and precipitation into the domestic water feed (especially above 2 mg/l copper), then the syndrome of blond hair turning green can occur, caused by green copper oxides being leached from pipework into the water.  Water hardness or the balanced process of water softening by ion exchange plays no real part in exceptional langelier swings, or copper deposition.

Copper deposition in feed water and heating systems may also become noticeably aggravated around seasonal weather shifts say from summer to autumn, august to september when heating systems are turned on more regularly and the weather becomes cold.  If water flows through domestic hot pipes feeding taps, showers etc, accelerate because of higher use (not the closed loop of a radiator / heating circuit so much) or additional domestic hot water looping pumps are used to effectively cause a higher water to copper contact where langelier is aggressive, then the syndrome of blonde hair turning green can be more noticeable.

The simplest water test done in seconds is with a copper test strip or more accurately water measured in the laboratory for copper, (something you probably may be aware of by the visibility of greenish blue staining).

The EU Drinking Water Directives safe level for copper in drinking water, and also the threshold often when stains can be observed is at 2 mg/L concentration.  If you have 3 mg/L you know you may have a problem, both for the safety of your drinking water if you don't have an RO water filter, and for the rescue of your household plumbing system probably valued at 10,000 euros or more to install, or much more to take out and then re-fit in extreme cases, where copper levels exceed 4 / 5 or 6 mg/L and very low LSI values are allowed to eat away at the plumbing system for enough years or decades.

Normally balanced hard water or very hard water with a near neutral LSI will not be expected to change radically after water is softened in 99%+ of cases as the ion exchange process will buffer a corresponding level of trace level sodium ions in low enough values to be safe for EU and HSE drinking water requirements but also will not radically affect LSI values.


Some of the factors that increase the corrosive potential of water are :

  1. accurately calculated Langelier Saturation Index (see table below)
  2. pH (lower than 6.5 or higher than 8.5)
  3. water flow rate (faster flow rate)
  4. daily water volume used (double or triple the normal water usage)
  5. water temperature (differences in temperatures affect LSI)
  6. dissolved gases (more dissolved gas)
  7. conductivity (differences in conductivity affect LSI)
  8. dissolved solids (differences in dissolved solids affect LSI)
  9. certain bacteria (bacteria and their off gassing or some odours (H2S) can affect corrosivity)
  10. suspended solids (more sediments or grit)
  11. chlorine / chloramine (many overly applied disinfection products can affect corrosivity)
  12. tannis / organic acids (tannis are humic and fulvic organic acids)
  13. quality of the grades of copper, lead, iron or stainless steel pipework used in plumbing (resistance to corrosivity of materials and the treatment of materials)
  14. the quantity of metal pipework used in the household plumbing system, and the distance water has to travel.
  15. bore size and inner surface area of the pipework system (larger metal bores and higher surface area in contact with aggressive water)
  16. the number of sharp elbows, or sweeping bends in pipework causing mechanical friction, especially if water contains abrasive sediments.
  17. galvanic corrosion though differences in electrical earth continuity or difference in metals in parts of the plumbing system


Saturation index values and the effect of corrosion potential or scaling potential

Langelier Index Description General Recommendation Risk
-5 Severe Corrosion Treatment Essential Plumbing Annihilation
-4 Severe Corrosion Treatment Essential Plumbing Annihilation
-3 Moderate Corrosion Treatment Recommended Longterm Pipe Death
-2 Moderate Corrosion Treatment Recommended Possible Trouble
-1 Milder Corrosion Treatment May Be Needed The Long Finger ?
-0.5 Milder Corrosion Treatment May Not Be Req. Hope All Goes Well
-0.3 None Mild Corrosion Probably No Treatment Looking Good
0 Near Balanced No Treatment Just right
0.3 Some Faint Coating Probably No Treatment Looking Good
0.5 Some Mild Coating Treatment May Not Be Needed Hope All Goes Well
1 Mild Scale Coating Treatment May Be Needed The Long Finger ?
2 Moderate Coating Treatment May Be Needed Possible Trouble
3 Moderate Coating Treatment Advisable Longterm Pipe Death
4 High Scale Coating Treatment Very Advisable Plumbing Annihilation

Potential for scaling

As it can be seen from the table above, hard water that acts hard by producing clearly visible limescale deposits in a short period of time, say in the higher cases found on water schemes and in wells in the West of Ireland at around 400 ppm of hardness, may in fact act a little differently from scheme to scheme and well to well, if the LSI value varies widely.

A water test report showing 200 ppm to 400 ppm of total hardness with expectations of highly problematic scaling, but with a balanced or mildly scaling Langelier Saturation Index, may show little or less concern during the daily household bathing, washing and cleaning chores on some rare schemes, however those schemes usually with 200 ppm to 400 ppm of total hardness will most likely have higher Langelier Saturation Index values and exhibit a much higher tendency for scaling and the subsequent signs of limescale formation throughout the plumbing system.

In rare cases, those households with 200 ppm to 400 ppm of total hardness (or lower) with a very high Langelier Saturation Index, can often demonstrate some of the most shocking levels of scale formation which can come about in some of the shortest periods of time, often resulting in the household copper cylinder getting choked up with limescale in one or two years, and the same for new electric showers only lasting one or two years, when a copper cylinders should have a lifetime span, and electric showers and washing machines should last in excess of 10 or 15 years in many cases on soft water especially with as close an LSI to zero.


Green hair

A common mistake made when guessing the cause of blonde hair turning green is chlorine in water or in swimming pools or after certain hair treatments, although excessive hair bleaching can increase hair damage and porosity and exposure to absorption of water borne metals.

The real cause is usually copper levels in water leaching from copper pipes, often in larger houses with a lot of copper pipework.  The level of copper in water that can turn hair green can be as low as 0.3 mg/l, but it is more likely when hair is porous or damaged often through over bleaching.

The cause of copper leaching from copper pipework is extensively described above, and although water testing may show pH levels as high as 8 pH and Langelier at a reasonable balance at the point of showering and bathing with minimal levels of copper, still if hair turns green then there is going to be some level of copper deposition in the water and it does not help if there is long term hair damage through bleaching where copper oxides coalesce with proteins in the hair.

By altering the balance of buffering agents in the water such as alkalinity and hardness to a measured level without over-hardeneing water, and using the correct water treatment (even after softened water), an increase in pH and Langelier will help to eradicate copper leaching however minimal or at higher levels.

The use of "chelating" hair shampoos after corrective water treatment once water is re-buffered and copper levels disappear, will rapidly sequester green colouring from blonde hair within a week or so.  A much rarer condition is orange hair from iron in water, which requires a different type of water treatment employing backwashable iron removal systems.

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