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The Langlier index or more properly the Langlier Saturation Index or LSI is defined and its use in evaluating the corrosivity of a water supply is explained.
This article series 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.
Langelier Index (LI). The LI is calculated using pH, temperature, total dissolved
solids, alkalinity, and total hardness. The LI is a measure of the balance between pH and calcium carbonate (CaCO3).
the LI value becomes more negative, the water is increasingly under-saturated with CaCO3 and therefore has increased
the LI value becomes
more positive, the water
is increasingly oversaturated
in CaCO3 precipitation
which can coat and protect
pipes from corrosion
but can cause scaling
in pipes, hot water
heaters, and fixtures. - Sigler & Bauder ret. 2016 cited at REFERENCES
On acidic well water and water corrosivity - using the Lange Saturation Index
It'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.
Water Corrosivity Action Levels in the Langelier (LSI) Index
The Langelier Index (LI), when calculated ranges from +4 through 0 to -5. Water with an LI above 0.5 (tending to form scale) or with an LI below -0.5 (tending to corrode metal pipes, tanks, etc), probably needs treatment.
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.
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 = very 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.
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.
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De Waard, C., and D. E. Milliams. "Carbonic acid corrosion of steel." Corrosion 31, no. 5 (1975): 177-181.
Isaac, R. A., L. Gil, A. N. Cooperman, K. Hulme, B. Eddy, M. Ruiz, K. Jacobson, C. Larson, and O. C. Pancorbo. "Corrosion in drinking water distribution systems: a major contributor of copper and lead to wastewaters and effluents." Environmental science & technology 31, no. 11 (1997): 3198-3203.
Jones, Anne. "Stress corrosion cracking." In in ASM Handbook, Metals Handbook. 1998.
Kermani, M. B., and A. Morshed. "Carbon dioxide corrosion in oil and gas production—a compendium." Corrosion 59, no. 8 (2003): 659-683.
Kiene, L., W. Lu, and Y. Levi. "Relative importance of the phenomena responsible for chlorine decay in drinking water distribution systems." Water Science and Technology 38, no. 6 (1998): 219-227.
Kritzer, Peter. "Corrosion in high-temperature and supercritical water and aqueous solutions: a review." The Journal of Supercritical Fluids 29, no. 1 (2004): 1-29.
Little, Brenda J., Florian B. Mansfeld, Peggy J. Arps, and James C. Earthman. Microbiologically influenced corrosion. Wiley‐VCH Verlag GmbH & Co. KGaA, 2007.
Oram, Brian, "Drinking Water Issues Corrosive Water (Lead, Copper, Aluminum, Zinc, and More)" (web page), Water Research Center, Water Research Center
B.F. Environmental Consultants Inc.
15 Hillcrest Drive, Dallas, PA 18612, USA, retrieved 2017/02/16, original source: http://www.water-research.net/index.php/drinking-water-issues-corrosive-water-lead-copper-aluminum-zinc-and-more
Roberge, P. R. (1999). Handbook of Corrosion Engineering (1st ed.). McGraw-Hill Professional. ISBN 0-07-076516-2.
Sigler, W. Adam, and Bauder, Jim, "CORROSIVITY" [PDF], Montana State University Extension, Water Quality Program, Department of Land Resources and Environmental Sciences, (un-dated) retrieved 2017/02/16, original source: http://waterquality.montana.edu/well-ed/files-images/Corrosivity.pdf - note that this page was adapted from Wilkes University Center For Environmental Quality;
Corrosion, Saturation Index, Balanced Water in Drinking Water Systems
Speller, Corrosion. Causes and Prevention of Corrosion in Steam and Hot Water Heating Systems. McGraw-Hill, 1951.
Volk, Christian, Esther Dundore, John Schiermann, and Mark LeChevallier. "Practical evaluation of iron corrosion control in a drinking water distribution system." Water research 34, no. 6 (2000): 1967-1974.
Was, G. S., P. Ampornrat, G. Gupta, S. Teysseyre, E. A. West, T. R. Allen, K. Sridharan et al. "Corrosion and stress corrosion cracking in supercritical water." Journal of Nuclear Materials 371, no. 1 (2007): 176-201.
 Clean Water Systems & Stores, Inc. 2806-A Soquel Ave, Santa Cruz, California 95062, Telephone: 1-888-600-5426 or international: 1-831-462-8500 . web search 4/23/12, original source: - cleanwaterstore.com/copper-pipe-corrosion.html
 "pH in Drinking-water Background document for development of WHO Guidelines for Drinking-water Quality", in Guidelines for drinking-water quality, 2nd ed. Vol. 2. Health criteria and other supporting information, World Health Organization, Geneva, 1996. Web search 4/23/12, original source: http://www.who.int/water_sanitation_health/dwq/chemicals/en/ph.pdf
 "Langelier Saturation Index (LSI), Wikipedia provided background information about some topics discussed at this website provided this citation is also found in the same article along with a " retrieved on" date. NOTE: because Wikipedia entries are fluid and can be amended in real time, we cite the retrieval date of Wikipedia citations and we do not assert that the information found there is necessarily authoritative.
 "Drinking Water Contaminants, List of Contaminants & their MCLs", U.S. EPA United States Environmental Protection Agency, National Primary Drinking Water Regulations, web search 4/23/12, original source: http://water.epa.gov/drink/contaminants/index.cfm#List
 "Basic Information about Copper in Drinking Water", U.S. EPA United States Environmental Protection Agency, web search 4/23/12, original source: http://water.epa.gov/drink/contaminants/basicinformation/copper.cfm
 "Fin Tube / Bare Elements", Slant/Fin Boilers & Baseboards, Slant/Fin Corporation, 100 Forest Drive, Greenvale, NY 11548, Phone: (516) 484-2600, Fax: (516) 484-5921, E-mail: email@example.com, web search 4/23/12, original source: http://www.slantfin.com/index.php/products/baseboard-residential/fin-tube--bare-elements
 Roger Hankey is principal of Hankey and Brown home inspectors, Eden Prairie, MN. Mr. Hankey is a past chairman of the ASHI Standards Committee. Mr. Hankey has served in other ASHI professional and leadership roles. Contact Roger Hankey at: 952 829-0044 - firstname.lastname@example.org. Mr. Hankey is a frequent contributor to InspectAPedia.com.
 Arlene Puentes, an ASHI member and a licensed home inspector in Kingston, NY, and has served on ASHI national committees as well as HVASHI Chapter President. Ms. Puentes can be contacted at email@example.com
 "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 , pp. 246-257(12), Maney Publishing, Quoting the article abstract:
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.
 "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. firstname.lastname@example.org, Water Sci Technol. 2004;49(2):55-62., Abstract
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.
Other water supply and drain piping and water pressure articles:
PB (polybutylene with mechanical fittings) Piping leaks: especially in mobile homes and in the U.S. South, for example trailers and double-wides throughout Florida that were piped with this material - per M Cramer. See , Journal of Light Construction, August 1996 [Technical Q&A].
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