කඨින ජලය is ජලය that has high ඛනිජ content (in contrast with මෘදු ජලය). Hard water minerals primarily consist of කැල්සියම් (Ca2+), and magnesium (Mg2+) metal cations, and sometimes other dissolved compounds such as bicarbonates and sulfates. Calcium usually enters the water as either කැල්සියම් කාබනේට් (CaCO3), in the form of limestone and chalk, or calcium sulfate (CaSO4), in the form of other mineral deposits. The predominant source of magnesium is dolomite (CaMg(CO3)2). Hard water is generally not harmful to one's health.
The simplest way to determine the hardness of water is the lather/froth test: soap or toothpaste, when agitated, lathers easily in soft water but not in hard water. More exact measurements of hardness can be obtained through a wet titration. The total water 'hardness' (including both Ca2+ and Mg2+ ions) is read as parts per million (ppm) or weight/volume (mg/L) of calcium carbonate (CaCO3) in the water. Although water hardness usually measures only the total concentrations of calcium and magnesium (the two most prevalent, divalent metal ions), iron, aluminium, and manganese may also be present at elevated levels in some geographical locations. Iron in this case is important for, if present, it will be in its tervalent form, causing the calcification to be brownish (the color of rust) instead of white (the color of most of the other compounds).
Hardness in water is defined as the presence of multivalent cations. Hardness in water can cause water to form scales and a resistance to soap. It can also be defined as water that does not produce lather with soap solutions, but produces white precipitate (scum). For example, sodium stearate reacts with calcium:
- 2C17H35COONa + Ca2+ → (C17H35COO)2Ca + 2Na+
Hardness of water may also be defined as the soap-consuming capacity of water, or the capacity of precipitation of soap as a characteristic property of water that prevents the lathering of soap.
Types of hard water[සංස්කරණය]
A distinction is made between 'temporary' and 'permanent' hard water.
Temporary hardness is caused by a combination of calcium ions and bicarbonate ions in the water. It can be removed by boiling the water or by the addition of lime (කැල්සියම් හයිඩ්රොක්සයිඩ්). Boiling promotes the formation of carbonate from the bicarbonate and precipitates calcium carbonate out of solution, leaving water that is softer upon cooling.
The following is the equilibrium reaction when කැල්සියම් කාබනේට් (CaCO3) is dissolved in water:
- CaCO3(s) + CO2(aq) + H2O ⇋ Ca2+(aq) + 2HCO3-(aq)
Upon heating, less CO2 is able to dissolve into the water (see Solubility). Since there is not enough CO2 around, the reaction cannot proceed from left to right, and therefore the CaCO3 will not dissolve as rapidly. Instead, the reaction is forced to the left (i.e., products to reactants) to re-establish equilibrium, and solid CaCO3 is formed. Boiling the water will remove hardness as long as the solid CaCO3 that precipitates out is removed. After cooling, if enough time passes, the water will pick up CO2 from the air and the reaction will again proceed from left to right, allowing the CaCO3 to "re-dissolve" into the water.
For more information on the solubility of calcium carbonate in water and how it is affected by atmospheric carbon dioxide, see කැල්සියම් කාබනේට්.
ස්ථිර කඨිනත්වය is hardness (mineral content) that cannot be removed by boiling. It is usually caused by the presence in the water of calcium and magnesium sulfates and/or chlorides which become more soluble as the temperature rises. Despite the name, permanent hardness can be removed using a water softener or ion exchange column, where the calcium and magnesium ions are exchanged with the sodium ions in the column.
Hard water causes scaling, which is the left-over mineral deposits that are formed after the hard water had evaporated. This is also known as limescale. The scale can clog pipes, ruin water heaters, coat the insides of tea and coffee pots, and decrease the life of toilet flushing units.
Similarly, insoluble salt residues that remain in hair after shampooing with hard water tend to leave hair rougher and harder to untangle.
In industrial settings, water hardness must be constantly monitored to avoid costly breakdowns in boilers, cooling towers, and other equipment that comes in contact with water. Hardness is controlled by the addition of chemicals and by large-scale softening with zeolite (Na2Al2Si2O8.xH2O) and ion exchange resins.
Because it is the precise mixture of minerals dissolved in the water, together with the water's pH and temperature, that determines the behavior of the hardness, a single-number scale does not adequately describe hardness. Descriptions of hardness correspond roughly with ranges of mineral concentrations:
|Moderately hard:||61-120 mg/L|
|Very hard:||>181 mg/L|
It is possible to measure the level of total hardness in water by obtaining a total hardness water testing kit. These kits measure the level of calcium and magnesium in the water. Temporary hardness test kits do not normally measure calcium and magnesium levels but normally use an approximation based on some form of alkalinity test. Measuring temporary hardness accurately would involve a series of tests to work out how much bicarbonates and carbonates are present and how much calcium and magnesium is present and what percentage combination there is. In most cases, the temporary hardness kit is a good approximation, but anions such as hydroxides, borates, phosphates can have quite an effect on temporary hardness test kits.
There are several different scales used to describe the hardness of water in different contexts.
- Parts per million (ppm)
Usually defined as one milligram of කැල්සියම් කාබනේට් (CaCO3) per litre of water (the definition used below).
- Grains per Gallon (gpg)
Defined as 1 grain (64.8 mg) of calcium carbonate per U.S. gallon (3.79 litres), or 17.118 ppm
- mmol/L (millimoles per litre)
One millimole of calcium (either Ca2+ or CaCO3) per litre of water corresponds to a hardness of 100.09 ppm or 5.608 dGH, since the molar mass of calcium carbonate is 100.09 g/mol.
- Degrees of General Hardness (dGH)
One degree of General Hardness is defined as 10 milligrams of calcium oxide per litre of water, which is the same as one German degree (17.848 ppm).
- Various alternative "degrees":
- Clark degrees (°Clark)/English degrees (°e or e)
One degree Clark is defined as one grain (64.8 mg) of calcium carbonate per Imperial gallon (4.55 litres) of water, equivalent to 14.254 ppm.
- German degrees (Deutsche Härte, °dH or dH)
One degree German is defined as 10 milligrams of calcium oxide per litre of water. This is equivalent to 17.848 milligrams of calcium carbonate per litre of water, or 17.848 ppm.
- French degrees (සැකිල්ල:Sic) (letter written in lower-case to avoid confusion with degree Fahrenheit — not always adhered to)
One degree French is defined as 10 milligrams of calcium carbonate per litre of water, equivalent to 10 ppm.
- American degrees
One degree American is defined as one milligram of calcium carbonate per litre of water, equivalent to 1 ppm.
- Clark degrees (°Clark)/English degrees (°e or e)
Although most of the above measures define hardness in terms of concentrations of calcium in water, any combination of calcium and magnesium cations having the same total molarity as a pure calcium solution will yield the same degree of hardness. Consequently, hardness concentrations for naturally occurring waters (which will contain both Ca2+ and Mg2+ ions), are usually expressed as an equivalent concentration of pure calcium in solution. For example, water that contains 1.5 mmol/L of elemental calcium (Ca2+) and 1.0 mmol/L of magnesium (Mg2+) is equivalent in hardness to a 2.5 mmol/L solution of calcium alone (250.2 ppm).
Several indices are used to describe the behaviour of calcium carbonate in water, oil, or gas mixtures.
Langelier Saturation Index (LSI)[සංස්කරණය]
The Langelier Saturation Index (sometimes Langelier Stability Index) is a calculated number used to predict the calcium carbonate stability of water. It indicates whether the water will precipitate, dissolve, or be in equilibrium with calcium carbonate. In 1936, Wilfred Langelier developed a method for predicting the pH at which water is saturated in calcium carbonate (called pHs). The LSI is expressed as the difference between the actual system pH and the saturation pH:
- LSI = pH (measured) - pHs
- For LSI > 0, water is super saturated and tends to precipitate a scale layer of CaCO3.
- For LSI = 0, water is saturated (in equilibrium) with CaCO3. A scale layer of CaCO3 is neither precipitated nor dissolved.
- For LSI < 0, water is under saturated and tends to dissolve solid CaCO3.
If the actual pH of the water is below the calculated saturation pH, the LSI is negative and the water has a very limited scaling potential. If the actual pH exceeds pHs, the LSI is positive, and being supersaturated with CaCO3, the water has a tendency to form scale. At increasing positive index values, the scaling potential increases.
In practice, water with an LSI between -0.5 and +0.5 will not display enhanced mineral dissolving or scale forming properties. Water with an LSI below -0.5 tends to exhibit noticeably increased dissolving abilities while water with an LSI above +0.5 tends to exhibit noticeably increased scale forming properties.
It is also worth noting that the LSI is temperature sensitive. The LSI becomes more positive as the water temperature increases. This has particular implications in situations where well water is used. The temperature of the water when it first exits the well is often significantly lower than the temperature inside the building served by the well or at the laboratory where the LSI measurement is made. This increase in temperature can cause scaling, especially in cases such as hot water heaters.
Ryznar Stability Index (RSI)[සංස්කරණය]
The Ryznar stability index (RSI) uses a database of scale thickness measurements in municipal water systems to predict the effect of water chemistry.
Ryznar saturation index (RSI) was developed from empirical observations of corrosion rates and film formation in steel mains. It is defined as:
- RSI = 2 pHs – pH (measured)
- For 6,5 < RSI < 7 water is considered to be approximately at saturation equilibrium with calcium carbonate
- For RSI > 8 water is under saturated and, therefore, would tend to dissolve any existing solid CaCO3
- For RSI < 6,5 water tends to be scale forming
Puckorius Scaling Index (PSI)[සංස්කරණය]
The Puckorius Scaling Index (PSI) uses slightly different parameters to quantify the relationship between the saturation state of the water and the amount of limescale deposited.
Some studies have shown a weak inverse relationship between water hardness and cardiovascular disease in men, up to a level of 170 mg calcium carbonate per litre of water. The World Health Organization has reviewed the evidence and concluded the data were inadequate to allow for a recommendation for a level of hardness.
In a review by František Kožíšek, M.D., Ph.D. National Institute of Public Health, Czech Republic there is a good overview of the topic which, unlike the WHO, sets some recommendations for the maximum and minimum levels of calcium (40-80 ppm) and magnesium (20-30 ppm) in drinking water, and a total hardness expressed as the sum of the calcium and magnesium concentrations of 2-4 mmol/L.
It is often considered desirable to soften hard water. This is because the calcium and magnesium causing hardness partly block the oil emulsifying action simple soap formulations use in the cleaning action. The calcium and magnesium form an insoluble precipitate observed as a soap scum and extra large amounts of soap have to be used to counteract this. Most modern soaps and detergents contain ingredients that at least partly prevent this effect and detergents are available that are chemically completely unaffected by the hardness. This makes hardness removal/softening an optional rather than a necessary water treatment except possibly in the case of extremely hard water. Where softening is practiced it is often recommended to soften only the water sent to domestic hot water systems so as to prevent or delay inefficiencies and damage due to scale formation in water heaters. Another reason for this is to avoid adding sodium or potassium from the softener to cold water taken for human consumption while still providing softening for hot water used in washing and bathing.
A water softener works on the principle of cation or ion exchange in which ions of the hardness minerals (mainly කැල්සියම් and magnesium ions) are exchanged for සෝඩියම් or potassium ions, effectively reducing the concentration of hardness minerals to tolerable levels and thus making the water softer and giving it a smoother feeling.
The most economical way to soften household water is with an ion exchange water softener. This unit uses sodium chloride (table salt) to recharge beads made of the ion exchange resins that exchange hardness mineral ions for sodium ions. Artificial or natural zeolites can also be used. As the hard water passes through and around the beads, the hardness mineral ions are preferentially absorbed, displacing the sodium ions. This process is called ion exchange. When the bead or sodium zeolite has a low concentration of sodium ions left, it is exhausted, and can no longer soften water. The resin is recharged by flushing (often back-flushing) with saltwater. The high excess concentration of sodium ions alter the equilibrium between the ions in solution and the ions held on the surface of the resin, resulting in replacement of the hardness mineral ions on the resin or zeolite with sodium ions. The resulting saltwater and mineral ion solution is then rinsed away, and the resin is ready to start the process all over again. This cycle can be repeated many times.
The discharge of brine water during this regeneration process has been banned in some jurisdictions (notably California, USA) due to concerns about the environmental impact of the discharged sodium.
Potassium chloride (softener salt substitute) may also be used to regenerate the resin beads. It exchanges the hardness ions for potassium. It also will exchange naturally occurring sodium for potassium resulting in sodium-free soft water.
Some softening processes in industry use the same method, but on a much larger scale. These methods create an enormous amount of salty water that is costly to treat and dispose of.
Temporary hardness, caused by hydrogen carbonate (or bicarbonate) ions, can be removed by boiling. For example, calcium bicarbonate, often present in temporary hard water, may be boiled in a kettle to remove the hardness. In the process, a scale forms on the inside of the kettle in a process known as "furring". This scale is composed of කැල්සියම් කාබනේට්.
- Ca(HCO3)2 → CaCO3 + CO2 + H2O
Hardness can also be reduced with a lime-soda ash treatment. This process, developed by Thomas Clark in 1841, involves the addition of slaked lime (calcium hydroxide — Ca(OH)2) to a hard water supply to convert the hydrogen carbonate hardness to carbonate, which precipitates and can be removed by filtration:
- Ca(HCO3)2 + Ca(OH)2 → 2CaCO3 + 2H2O
The addition of sodium carbonate also permanently softens hard water containing calcium sulfate, as the calcium ions form calcium carbonate which precipitates out and potasium sulphate is formed which is soluble. The calcium carbonate that is formed sinks to the bottom. Sodium sulfate has no effect on the hardness of water.
- Na2CO3 + CaSO4 → Na2SO4 + CaCO3
Effects on skin[සංස්කරණය]
Some confusion may arise after a first experience with soft water. Hard water does not lather well with soap and leaves a "clean" feeling. Soft water lathers better than hard water but leaves a "slippery feeling" on the skin after use with soap. Some providers of water softening equipment claim that the "slippery feeling" after showering in soft water is due to "clean skin" and the absence of 'friction-causing' soap scum.
However, the chemical explanation is that softened water, because of its sodium content, has a much reduced ability to combine with the soap film on the body; therefore, the soap is much more difficult to rinse off. Solutions are to use less soap or a synthetic liquid body wash.
Hard water in Australia[සංස්කරණය]
Analysis of water hardness in major Australian cities by the Australian Water Association shows a range from very soft (Melbourne) to very hard (Adelaide). Total Hardness levels of Calcium Carbonate in ppm are: Canberra: 40; Melbourne: 10 - 26; Sydney: 39.4 – 60.1; Perth: 29 – 226; Brisbane: 100; Adelaide: 134 – 148; Hobart: 5.8 – 34.4; Darwin: 31.
Hard water in Canada[සංස්කරණය]
Prairie provinces (mainly Saskatchewan and Manitoba) contain high quantities of calcium and magnesium, often as dolomite, which are readily soluble in the groundwater that contains high concentrations of trapped carbon dioxide from the last glaciation. In these parts of Canada, the total hardness in ppm of calcium carbonate equivalent frequently exceed 200 ppm, if groundwater is the only source of potable water. The west coast, by contrast, has unusually soft water, derived mainly from mountain lakes fed by glaciers and snowmelt.
Some typical values are: Montreal 116 ppm, Calgary 165 ppm, Regina 202 ppm, Saskatoon < 140 ppm, Winnipeg 77 ppm, Toronto 121 ppm, Vancouver < 3 ppm, Charlottetown PEI 140 – 150 ppm.
Hard water in England and Wales[සංස්කරණය]
Information from the British Drinking Water Inspectorate shows that drinking water in England is generally considered to be 'very hard', with most areas of England, particularly east of a line between the Severn and Tees estuaries, exhibiting above 200 ppm for the calcium carbonate equivalent. Wales, Devon, Cornwall and parts of North-West England are softer water areas, and range from 0 to 200 ppm. In the brewing industry in England and Wales, water is often deliberately hardened with gypsum in the process of Burtonisation.
Hard water in the United States[සංස්කරණය]
More than 85% of American homes have hard water. The softest waters occur in parts of the New England, South Atlantic-Gulf, Pacific Northwest, and Hawaii regions. Moderately hard waters are common in many of the rivers of the Tennessee, Great Lakes, Pacific Northwest, and Alaska regions. Hard and very hard waters are found in some of the streams in most of the regions throughout the country. Hardest waters (greater than 1,000 ppm) are in streams in Texas, New Mexico, Kansas, Arizona, and southern California.
- USGS Water-Quality Information: Water Hardness and Alkalinity
- Definitions of units of measure for water hardness
- Corrosion by water
- T.E., Larson and R. V. Skold, Laboratory Studies Relating Mineral Quality of Water to Corrosion of Steel and Cast Iron, 1958 Illinois State Water Survey, Champaign, IL pp.  - 46: ill. ISWS C-71
- Stiff, Jr., H.A., Davis, L.E., A Method For Predicting The Tendency of Oil Field Water to Deposit Calcium Carbonate, Pet. Trans. AIME 195;213 (1952).
- Oddo,J.E., Tomson, M.B.,Scale Control, Prediction and Treatment Or How Companies Evaluate A Scaling Problem and What They Do Wrong, CORROSION/92, Paper No. 34, (Houston, TX:NACE INTERNATIONAL 1992).
- World Health Organization Hardness in Drinking-Water, 2003
- František Kožíšek Health significance of drinking water calcium and magnesium, February 2003
- Pocock SJ, Shaper AG, Packham RF (April 1981). "Studies of water quality and cardiovascular disease in the United Kingdom". Sci. Total Environ. 18: 25–34. doi:10.1016/S0048-9697(81)80047-2. PMID 7233165.
- Marque S, Jacqmin-Gadda H, Dartigues JF, Commenges D (2003). "Cardiovascular mortality and calcium and magnesium in drinking water: an ecological study in elderly people". Eur. J. Epidemiol. 18 (4): 305–9. doi:10.1023/A:1023618728056. PMID 12803370. http://www.kluweronline.com/art.pdf?issn=0393-2990&volume=18&page=305.
- Rubenowitz E, Axelsson G, Rylander R (January 1999). "Magnesium and calcium in drinking water and death from acute myocardial infarction in women". Epidemiology 10 (1): 31–6. doi:10.1097/00001648-199901000-00007. PMID 9888277. http://meta.wkhealth.com/pt/pt-core/template-journal/lwwgateway/media/landingpage.htm?issn=1044-3983&volume=10&issue=1&spage=31.
- BBC News. Water softener eczema relief hope
- How does a water softener work? at Howstuffworks.com
- With soft water, why can't we rinse off all the soap?
- ACTewAGL: Dishwashers and Water Hardness
- Melbourne Water Public Health Compliance Report – July-September 2006
- Sydney Typical Drinking Water Analysis
- Perth Drinking Water Quality Annual report 2005-06
- Brisbane Drinking Water
- Adelaide Water Quality
- Hobart Drinking Water Quality
- Darwin Water Quality
- 2006 Winnipeg drinking water quality test results
- City of Toronto: Toronto Water – FAQ
- GVRD Wash Smart – Water Facts
- Wilson, Amber; Parrott, Kathleen; Ross, Blake (1999-06). "Household Water Quality – Water Hardness". http://www.ext.vt.edu/pubs/housing/356-490/356-490.html. සම්ප්රවේශය කෙරුණු දිනය 2009-04-26.
- Briggs, J.C., and Ficke, J.F.; Quality of Rivers of the United States, 1975 Water Year -- Based on the National Stream Quality Accounting Network (NASQAN): U.S. Geological Survey Open-File Report 78-200, 436 p. (1977)
32. www.water.com by Basha