- tough called water with a high salt content
- soft with little content
- temporary (carbonate) hardness, - due to bicarbonates of calcium and magnesium Ca (HCO 3) 2; Mg (HCO 3) 2,
- permanent (non-carbonate) hardness - caused by the presence of other salts that are not released when water is boiled: mainly sulfates and chlorides Ca and Mg (CaSO 4, CaCl 2, MgSO 4, MgCl 2).
Water hardness standards - in 99.99% of cases we are talking about temporary hardness, VST data:
|
Water hardness adopted in the Russian Federation |
US water hardness |
||||||||
|
°F = |
ppm = mg/l |
gpg |
°F = |
ppm = mg/l |
gpg |
||||
|
1. Soft water |
< 5,608 °dGH |
Soft water = Soft water |
< 3,361 °dGH |
||||||
|
2. Water of medium hardness |
5.608 - 28.04°dGH |
Medium hardness water = Moderate hardness water |
3.361 - 6.724°dGH |
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|
3. Hard water |
Hard water = Hard hardness water |
6.724-10.085°dGH |
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|
Very hard water = Very Hard hardness water |
> 10.085°dGH |
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Comparison of accepted water hardness standards in the Russian Federation and Europe (Germany), Ecoline data:
Water hardness in some cities of the world- MVC data - unknown reliability :)
| Hardness, °F | Calcium, mg/l | Magnesium, mg/l | |
|---|---|---|---|
| Moscow | 2,0-5,5 | 46 | 11 |
| Paris | 5,0-6,0 | 90 | 6 |
| Berlin | 5,0-8,8 | 121 | 12 |
| New York | 0,3-0,4 | 6 | 1 |
| Sydney | 0,2-1,3 | 15 | 4 |
- World Health Organization (WHO) recommendations for drinking water:
- calcium - 20-80 mg/l; magnesium - 10-30 mg / l. There is no recommended value for stiffness. According to these indicators, Moscow drinking water complies with WHO recommendations.
- Russian regulatory documents (SanPiN 2.1.4.1074-01 and GN 2.1.5.1315-03) for drinking water regulate:
- calcium - the standard is not established; magnesium - no more than 50 mg/l; rigidity - no more than 7 ° Zh.
- Standard for the physiological usefulness of bottled water (SanPiN 2.1.4.1116-02):
- calcium - 25-130 mg/l; magnesium - 5-65 mg/l; hardness - 1.5-7 ° W.
- According to the content of calcium and magnesium, bottled water of the highest category is officially no better than tap water.
Translation of units and degrees of water hardness - in 99.99% of cases we are talking about temporary hardness:
| °F = 1 meq/l |
mmol/L | ppm, mg/L | dGH, °dH | gpg | °e, °Clark | °fH | |
| 1 Russian °F \u003d 1 mg-eq / l is: | 1 | 0,5 | 50,05 | 2,804 | 2,924 | 3,511 | 5,005 |
|---|---|---|---|---|---|---|---|
| 1 mmol/L = mmol/L is: | 2 | 1 | 100.1 | 5.608 | 5.847 | 7.022 | 10.01 |
| 1 US ° ppm w = mg/L = American degre: | 0,01998 | 0.009991 | 1 | 0.05603 | 0.05842 | 0.07016 | 0.1 |
| 1 German ° dGH, °dH is: | 0,3566 | 0.1783 | 17.85 | 1 | 1.043 | 1.252 | 1.785 |
| 1 US popular unit gpg is: |
0,342 | 0.171 | 17.12 | 0.9591 | 1 | 1.201 | 1.712 |
| 1 English °e, °Clark is: | 0,2848 | 0.1424 | 14.25 | 0.7986 | 0.8327 | 1 | 1.425 |
| 1 french °fH is: | 0,1998 | 0.09991 | 10 | 0.5603 | 0.5842 | 0.7016 | 1 |
| Example: 1 °F = 50.05 ppm | |||||||
- American degrees of water hardness, attention here two points:
- gpg = Grains per Gallon: 1 (0.0648 g) CaCO 3 in 1 (3.785 L) water. Dividing grams by liters, we get: 17.12 mg / l CaCO 3 - this is not an "American degree", but a value of water hardness that is very used in the states.
- American degree = w = mg/L = American degre: 1 part CaCO 3 in 1,000,000 parts water 1 mg/l CaCO 3
- English degrees of water hardness = °e = °Clark: 1 (0.0648 g) in 1 (4.546) L of water = 14.254 mg/L CaCO 3
- French degrees of water hardness (°fH or °f)(fh): 1 part CaCO 3 in 100,000 parts water, or 10 mg/l CaCO 3
- German degrees of water hardness = °dH (deutsche Härte = "German hardness" can be °dGH (total hardness) or °dKH (for carbonate hardness)): 1 part calcium oxide - CaO in 100,000 parts of water, or 0.719 parts of magnesium oxide - MgO in 100,000 parts of water, which gives 10 mg/l CaO or 7.194 mg/l MgO
- Russian (RF) degree of water hardness ° W = 1 mg-eq / l: corresponds to an alkaline earth concentration numerically equal to 1/2 of its millimole per liter, which gives 50.05 mg/l CaCO 3 or 20.04 mg/l Ca2+
- mmol/L = mmol/L: corresponds to the concentration of the alkaline earth element, numerically equal to 100.09 mg/l CaCO 3 or 40.08 mg/l Ca2+
Methods for eliminating water hardness
- Thermal softening. Based on boiling water, as a result, thermally unstable calcium and magnesium bicarbonates decompose with the formation of scale:
- Ca(HCO 3) 2 → CaCO 3 ↓ + CO 2 + H 2 O.
- Boiling removes only temporary (carbonate) hardness. Finds application in everyday life.
- Reagent softening. The method is based on adding soda ash Na2CO3 or slaked lime Ca(OH)2 to water. In this case, calcium and magnesium salts pass into insoluble compounds and, as a result, precipitate. For example, the addition of slaked lime results in the conversion of calcium salts into insoluble carbonate:
- Ca(HCO 3) 2 + Ca(OH) 2 → 2CaCO 3 ↓ + 2H 2 O
- The best reagent for eliminating general water hardness is sodium orthophosphate Na3PO4, which is part of most household and industrial preparations:
- 3Ca(HCO 3)2 + 2Na 3 PO4 → Ca 3 (PO4)2↓ + 6NaHCO 3
- 3MgSO 4 + 2Na 3 PO 4 → Mg 3 (PO 4) 2 ↓ + 3Na 2 SO 4
- Orthophosphates of calcium and magnesium are very poorly soluble in water, so they are easily separated by mechanical filtration. This method is justified at relatively high water consumption, since it is associated with the solution of a number of specific problems: sediment filtration, accurate dosage of the reagent.
- cationization. The method is based on the use of ion-exchange granular loading (most often ion-exchange resins). Such loading, upon contact with water, absorbs cations of hardness salts (calcium and magnesium, iron and manganese). Instead, depending on the ionic form, it releases sodium or hydrogen ions. These methods are respectively called Na-cationization and H-cationization.
- With a properly selected ion-exchange load, water hardness decreases with single-stage sodium cationization to 0.05-0.1 °F, with two-stage - up to 0.01 °F.
- In industry, with the help of ion-exchange filters, calcium and magnesium ions are replaced with sodium and potassium ions, obtaining soft water.
- Reverse osmosis. The method is based on the passage of water through semi-permeable membranes (usually polyamide). Together with hardness salts, most other salts are also removed. The cleaning efficiency can reach 99.9%.
- There are nanofiltration (the conditional diameter of the membrane holes is equal to units of nanometers) and picofiltration (the conditional diameter of the membrane holes is equal to units of picometers).
- The disadvantages of this method should be noted:
- - the need for preliminary preparation of water supplied to the reverse osmosis membrane;
- - relatively high cost of 1 liter of produced water (expensive equipment, expensive membranes);
- - low salinity of the received water (especially during picofiltration). The water becomes almost distilled.
- Electrodialysis. It is based on the removal of salts from water under the action of an electric field. Removal of ions of dissolved substances occurs due to special membranes. As well as when using reverse osmosis technology, other salts are removed, in addition to hardness ions.
- Distillation: It is possible to completely purify water from hardness salts distillation.
"Hard" water- one of the most common problems, both in country houses with autonomous water supply, and in city apartments with centralized water supply. The degree of hardness depends on the presence of calcium and magnesium salts (hardness salts) in the water and is measured in milligram equivalent per liter (mg-eq / l). According to the American classification (for drinking water), with a hardness content of less than 2 mg-eq / l, water is considered “soft”, from 2 to 4 mg-eq / l - normal (we repeat, for food purposes!), From 4 to 6 mg -eq/l - hard, and over 6 mg-eq/l - very hard.
For many applications, water hardness does not play a significant role (for example, for extinguishing fires, watering the garden, cleaning streets and sidewalks). But in some cases, rigidity can create problems. When taking a bath, washing dishes, doing laundry, washing a car, hard water is much less effective than soft water. And that's why:
When using soft water, 2 times less detergent is consumed;
Hard water, interacting with soap, forms “soap slags” that are not washed off with water and leave unsympathetic stains on dishes and plumbing surfaces; "Soap slags" are also not washed off the surface of human skin, clogging pores and covering every hair on the body, which can cause rashes, irritation, itching;
When water is heated, the hardness salts contained in it crystallize, falling out in the form of scale. Scale is the cause of 90% of failures in water heating equipment. Therefore, water heated in boilers, boilers, etc., is subject to an order of magnitude more stringent requirements for hardness;
In many industrial processes, hardness salts can react chemically to form unwanted intermediates.
The concept of rigidity
Water hardness is usually associated with calcium cations (Ca 2+) and, to a lesser extent, magnesium (Mg 2+). In fact, all divalent cations affect hardness to some extent. They interact with anions, forming compounds (hardness salts) capable of precipitating. Monovalent cations (for example, sodium Na +) do not have this property.
This table lists the main metal cations that cause hardness and the main anions with which they are associated.
In practice, strontium, iron, and manganese have such a small effect on stiffness that they are usually neglected. Aluminum (Al3+) and ferric iron (Fe3+) also contribute to hardness, but at the pH levels found in natural waters, their solubility, and thus "contribution" to hardness, is negligible. Similarly, the insignificant effect of barium (Ba2+) is not taken into account.
Types of stiffness
General hardness. It is determined by the total concentration of calcium and magnesium ions. It is the sum of carbonate (temporary) and non-carbonate (permanent) hardness.
carbonate hardness. It is caused by the presence of bicarbonates and carbonates (at pH> 8.3) of calcium and magnesium in the water. This type of hardness is almost completely eliminated when water is boiled and is therefore called temporary hardness. When water is heated, bicarbonates decompose with the formation of carbonic acid and precipitation of calcium carbonate and magnesium hydroxide.
non-carbonate hardness. It is caused by the presence of calcium and magnesium salts of strong acids (sulphuric, nitric, hydrochloric) and is not eliminated by boiling (constant hardness).
Units
In world practice, several units of measurement of stiffness are used, all of them in a certain way correlate with each other. In Russia, the Gosstandart sets the mole per cubic meter (mol/m3) as the unit of water hardness.
One mole per cubic meter corresponds to a mass concentration of equivalents of calcium ions (1/2 Ca2+) 20.04 g/m3 and magnesium ions (1/2Mg2+) 12.153 g/m3. The numerical value of hardness, expressed in moles per cubic meter, is equal to the numerical value of hardness, expressed in milliequivalents per liter (or cubic decimeter), i.e. 1mol/m3=1mmol/l=1mg-eq/l=1mg-eq/dm3.
In addition, hardness units such as German degrees (do, dH), French degrees (fo), American degrees, ppm CaCO3 are widely used in foreign countries.
The ratio of these stiffness units is presented in the following table:
Note: One German degree corresponds to 10 mg/dm3 CaO or 17.86 mg/dm3 CaCO3 in water. One French degree corresponds to 10 mg/dm3 CaCO3 in water. One US degree corresponds to 1 mg/dm3 of CaCO3 in water.
Origin of stiffness
Ions of calcium (Ca2+) and magnesium (Mg2+), as well as other alkaline earth metals that cause hardness, are present in all mineralized waters. Their source is natural deposits of limestone, gypsum and dolomite. Calcium and magnesium ions enter the water as a result of the interaction of dissolved carbon dioxide with minerals and other processes of dissolution and chemical weathering of rocks. Microbiological processes occurring in soils in the catchment area, in bottom sediments, as well as wastewater from various enterprises can also serve as a source of these ions.
Water hardness varies widely and there are many types of water classifications according to the degree of its hardness.
Usually, in low-mineralized waters, hardness due to calcium ions prevails (up to 70%-80%) (although in some rare cases magnesium hardness can reach 50-60%). With an increase in the degree of mineralization of water, the content of calcium ions (Ca2+) drops rapidly and rarely exceeds 1 g/l. The content of magnesium ions (Mg2+) in highly mineralized waters can reach several grams, and in salt lakes - tens of grams per liter of water.
In general, surface water hardness is generally less than groundwater hardness. The hardness of surface waters is subject to noticeable seasonal fluctuations, usually reaching its highest value at the end of winter and the lowest during the flood period, when it is abundantly diluted with soft rain and melt water. Sea and ocean water have very high hardness (tens and hundreds of meq/dm3)
Influence of stiffness
From the point of view of drinking water use, its acceptability in terms of hardness can vary significantly depending on local conditions. The taste threshold for the calcium ion lies (in terms of mg-equivalent) in the range of 2-6 meq/l, depending on the corresponding anion, and the taste threshold for magnesium is even lower. In some cases, water with hardness above 10 meq/l is acceptable to consumers. High hardness worsens the organoleptic properties of water, giving it a bitter taste and having a negative effect on the digestive organs.
The World Health Organization does not offer any recommended hardness for health reasons. The WHO materials state that although a number of studies have found a statistically inverse relationship between the hardness of drinking water and cardiovascular diseases, the available data are not sufficient to conclude that this relationship is causal. Similarly, soft water has not been unequivocally proven to have a negative effect on the balance of minerals in the human body.
However, depending on pH and alkalinity, water with a hardness above 4 mEq/L can cause deposits of slag and scale (calcium carbonate) in the distribution system, especially when heated. That is why the norms of the Boiler Supervision introduce very strict requirements for the hardness of the water used to feed the boilers (0.05-0.1 mg-eq / l).
In addition, when hardness salts interact with detergents (soap, washing powders, shampoos), “soap slags” are formed in the form of foam. This leads not only to a significant waste of detergents. After drying, such foam remains in the form of a plaque on plumbing, underwear, human skin, and hair (an unpleasant feeling of “hard” hair is well known to many). The main negative impact of these toxins on a person is that they destroy the natural fatty film, which is always covered with normal skin and clog its pores. A sign of such a negative impact is the characteristic "creak" of cleanly washed skin or hair. It turns out that the irritating “soapy” feeling that some people experience after using soft water is a sign that the protective fatty film on the skin is safe and sound. She is the one who slides. Otherwise, you have to spend money on lotions, softening and moisturizing creams and other tricks to restore the skin protection that Mother Nature already provided us with.
At the same time, it is necessary to mention the other side of the coin. Soft water with a hardness of less than 2 meq/l has a low buffer capacity (alkalinity) and may, depending on the pH level and a number of other factors, have an increased corrosive effect on water pipes. Therefore, in a number of applications (especially in heat engineering), it is sometimes necessary to carry out special water treatment in order to achieve an optimal ratio between water hardness and its corrosiveness.
Water hardness is a property due to the presence of dissolved salts in water, mainly calcium and magnesium. Water hardness is divided into carbonate (the presence of magnesium and calcium bicarbonates in it) and non-carbonate (the presence of salts of strong acids - chlorides or sulfates of calcium and magnesium). The sum of carbonate and non-carbonate hardness determines the total hardness.
Carbonate hardness is called temporary, since with prolonged boiling of such water, bicarbonates decompose with the formation of a precipitate of calcium carbonate and the release of carbon dioxide:
Ca (HCO 3) 2 \u003d CaCO 3 + CO 2 + H 2 O
Mg (HCO 3) 2 \u003d Mg (OH) 2 ↓ + 2CO 2
The hardness of water, due to the presence of magnesium and calcium sulfates, is called constant. It can only be eliminated chemically:
CaSO 4 + Na 2 CO 3 \u003d CaCO 3 ↓ + Na 2 SO 4.
Currently, ion exchange resins are also used to eliminate stiffness.
Ways to eliminate water hardness
Calcium and magnesium salts are dissolved in natural water. These are hydrocarbons and sulfates. We will show two methods for the precipitation of hydrocarbonates to reduce the hardness of water. The first way is boiling. Boiling* converts soluble hydrocarbons into insoluble carbonates and the hardness of the water decreases.
Witha(HCO 3 ) 2 = CaCO 3 ↓+H 2 O+CO 2
The second way is to add lime water. When lime water is added, bicarbonates turn into carbonates and the water becomes softer.
Witha(HCO 3 ) 2 + Ca(OH) 2 = CaCO 3 ↓+2H 2 O
But water hardness also depends on calcium and magnesium sulfates. Calcium and magnesium sulfates can be removed with sodium carbonate. When sodium carbonate is added, sulfates are converted to insoluble calcium and magnesium carbonates.
CaSO 4 + Na 2 CO 3 = CaCO 3 ↓+ Na 2 SO 4
Water softening
The removal of hardness salts from water, i.e., its softening, must be carried out to feed boiler plants, and water hardness for medium and low pressure boilers should be no more than 0.3 mg-eq / l. Softening water is also required for such industries as textile, paper, chemical, where water should have a hardness of not more than 0.7 -1.0 mg-eq / l. Softening of water for domestic and drinking purposes is also advisable, especially if it exceeds 7 mg-eq / l. The following main methods of water softening are used:
reagent method - by introducing reagents that contribute to the formation of poorly soluble calcium and magnesium compounds and their precipitation;
cationic method, in which softened water is filtered through substances that have the ability to exchange the cations (sodium or hydrogen) contained in them for calcium and magnesium cations, salts dissolved in water. And as a result of the exchange, calcium and magnesium ions are retained and sodium salts are formed that do not give water hardness;
thermal method, which consists in heating water to a temperature above 100 °, while carbonate hardness salts are almost completely removed.
Often, softening methods are used in combination. For example, some of the hardness salts are removed by the reagent method, and the rest by cation exchange. Of the reagent methods, the soda-lime softening method is the most common. Its essence is reduced to obtaining, instead of Ca Mg salts dissolved in water, insoluble CaCO3 and Mg (OH) 2 salts that precipitate. Both reagents - soda Na2CO3 and lime Ca(OH)2 - are introduced into the softened water simultaneously or alternately. Salts of carbonate, temporary hardness are removed with lime, non-carbonate, constant hardness - soda. Chemical reactions when removing carbonate hardness proceed as follows:
Ca(HCO3)2 + Ca(OH)2 = 2CaCO3 + 2H2O
Magnesium oxide hydrate Mg(OH)2 coagulates and precipitates. To eliminate non-carbonate hardness, Na2CO3 is introduced into the softened water. The chemical reactions when removing non-carbonate hardness are as follows:
Na2CO3 + CaSO4 = CaCO3 + Na2SO4;
Na2CO3 + CaC12 = CaCO3 + 2NaCl.
As a result of the reaction, calcium carbonate is obtained, which precipitates. Reagents used in water treatment are introduced into the water in the following places:
a) chlorine (in case of preliminary chlorination) - into the suction pipelines of the pumping station of the first lift or into the conduits supplying water to the treatment station;
b) coagulant - into the pipeline before the mixer or into the mixer;
c) lime for alkalization during coagulation - simultaneously with the coagulant;
d) activated carbon to remove odors and tastes in water up to 5 mg/l - before filters. At high doses, coal should be introduced at the pumping station of the first lift or simultaneously with the coagulant into the mixer of the water treatment plant, but not earlier than 10 minutes after the introduction of chlorine;
e) chlorine and ammonia for water disinfection are introduced to treatment facilities and into filtered water. In the presence of phenols in the water, ammonia should be introduced both during preliminary and final chlorination.
Special types of water purification and treatment include desalination, desalination, iron removal, removal of dissolved gases from water and stabilization.
One of the most frequently asked questions by residents of the city of Moscow is the question of the hardness of drinking water. This is due to the widespread use of dishwashers and washing machines in everyday life, for which the calculation of the load of detergents is based on the actual value of the hardness of the water used.
You can find out the value of water hardness at your address using our electronic service
In Russia, hardness is measured in "degrees of hardness", and global manufacturers use units of measurement accepted in their countries. Therefore, for the convenience of residents, a "Stiffness Calculator" has been created, with which you can convert the stiffness values from one measurement system to another in order to properly set up your household appliances.
| Rigidity index | Current unit of measurement | Required unit of measure | The result of calculating the indicator | |
|---|---|---|---|---|
| = |
Hardness is a set of water properties associated with the content of dissolved salts in it, mainly calcium and magnesium ("hardness salts"). The total stiffness consists of temporary and permanent. Temporary hardness can be eliminated by boiling water, which is due to the property of some salts to precipitate, forming the so-called scale.
The main factor influencing the value of hardness is the dissolution of rocks containing calcium and magnesium (limestone, dolomite) when natural water passes through them. Surface waters are generally softer than groundwater. The hardness of surface waters is subject to noticeable seasonal fluctuations, reaching a maximum in winter. The minimum values of hardness are typical for periods of high water or high water, when there is an intensive flow of soft melt or rainwater into the water supply sources.
Rigidity units
In Russia, hardness is measured in "degrees of hardness" (1°W = 1 meq/l = 1/2 mol/m3). Abroad, other units of measurement of water hardness are accepted.
Rigidity units
1 ° W \u003d 20.04 mg Ca 2 + or 12.15 Mg 2 + in 1 dm 3 of water;
1°DH = 10 mg CaO in 1 dm 3 of water;
1°Clark = 10 mg CaCO 3 in 0.7 dm 3 water;
1°F = 10 mg CaCO 3 in 1 dm 3 water;
1 ppm \u003d 1 mg CaCO 3 in 1 dm 3 of water.
Water hardness in some cities of the world
World Health Organization (WHO) recommendations for drinking water:
calcium - 20-80 mg / l; magnesium - 10-30 mg / l. There is no recommended value for stiffness. According to these indicators, Moscow drinking water complies with WHO recommendations.
Russian regulatory documents (SanPiN 2.1.4.1074-01 and GN 2.1.5.1315-03) for drinking water regulate:
calcium - the standard is not established; magnesium - no more than 50 mg / l; rigidity - no more than 7 ° Zh.
The degree of hardness of water is determined by the presence of ions in water calcium (Ca 2+), magnesium (Mg 2+), strontium (Sr 2+), barium (Ba 2+), iron (Fe 2+), manganese (Mn 2+). Moreover, the content of calcium and magnesium ions significantly exceed the concentrations of the other listed ions combined. Therefore, in Russia it is customary to determine the value of hardness as the sum of calcium and magnesium ions contained in water, expressed in milligram equivalents per liter (mg-eq / l). One meq/l corresponds to the content of 20.04 mg Ca 2+ or 12.16 mg Mg 2+ per liter of water.
There are carbonate (temporary, eliminated by boiling) and non-carbonate (permanent) hardness. Carbonate hardness is due to the presence of calcium and magnesium bicarbonates in water, non-carbonate hardness is due to the presence of sulfates, chlorides, silicates, nitrates and phosphates of these metals.
Temporary hardness is called because when boiled, calcium and magnesium bicarbonates decompose and precipitate in the form of carbonates. The chemical reaction of this process is as follows: 
Ca(HCO 3) 2 - t o C → CaCO 3↓ + H 2 O + CO 2
Mg(HCO 3) 2 - t o C → CaCO 3↓ + H 2 O + CO 2
The resulting precipitate forms a plaque (so-called scale) on the walls of the dishes in which water is boiled. After boiling and precipitation of hydrocarbons, the water becomes softer.
Permanent hardness is due to the presence in water of stable chemical compounds of sulfates, chlorides, silicates and some other salts of calcium and magnesium, which do not precipitate and are not removed when boiled. The sum of the temporary and permanent hardness gives the total hardness of the water.
General water hardness, standards
The world practice of quality control of water consumed for drinking (World Health Organization (WHO) standards, European Union (EU) standards, ISO standards, as well as US standards) do not standardize the hardness of drinking water - only separately the content of calcium and magnesium ions in water. According to Russian standards (), hardness should not exceed 7 mg-eq / l. What happens when this value is exceeded? It turns out that when water hardness is above 7 mg-eq/l, the rate of overgrowing of pipes with lime deposits increases significantly, which reduces their service life and increases operating costs. And at very low water hardness, it acquires strong corrosive properties. The active use of plastic and metal-plastic in recent years allows you to remove restrictions on the use of soft water.
General water hardness, classifications
Classifications of natural water according to the degree of hardness differ in different countries, and can also be subdivided depending on the purpose of using water.
The most general classification is as follows:
According to the American classification, drinking water is considered “soft” when the content of hardness salts is less than 2 mg-eq / l, normal - from 2 to 4 mg-eq / l, hard - from 4 to 6 mg-eq / l, and very hard - over 6 meq/l. It should be noted that such a classification is valid for water used for drinking purposes. The water in hot water systems and in contact with any heating elements must be softer for the normal functioning of the system. Here you can not do without installing, in particular -. At the same time, if the water comes from a private well, it is likely that a preliminary one will be required.
Detergent waste
In hard water from ordinary soap (in the presence of calcium ions), soap slags are formed - insoluble compounds that do not carry any useful functions. And until all the calcium hardness of the water is eliminated in this way, the formation of foam will not begin. There is a significant waste of detergents. After drying, such soap slags remain in the form of a plaque on plumbing, linen, human skin and hair (an unpleasant feeling of “hard” hair is well known to many).
Negative effect on tissues
Hard water is not suitable for washing and washing. Why? When soap or powder comes into contact with hard water, cations of hardness salts (Ca 2+, Mg 2+, Fe 2+) react with fatty acid anions that are part of the soap and form poorly soluble compounds, such as calcium stearate Ca (C 17 H 35 COO) 2. These deposits gradually clog the pores of the fabric and it ceases to allow air and moisture to pass through, the fibers become coarse and inelastic. The colors of the product fade and acquire a gray-yellow tint. “Lime soaps” that have settled on the fabric deprive it of its strength.
Skin irritation
When “hardness flakes” get on human skin, the natural fatty film is destroyed, which protects the skin from the adverse effects of the environment, and pores are also clogged. A sign of such a negative impact is the characteristic “creak” of the skin or hair that appears after taking a shower. In fact, the “soapiness” that causes irritation in some people after using soft water is a sure sign that the protective fatty film on the skin is safe and sound. She is the one who slides. Or use hard water and compensate for the violation of the coating with lotions, softening and moisturizing creams and other tricks to restore the skin protection that nature has already provided us with.
Reduced equipment life
When water with a hardness of more than 4 mg-eq / l is heated against the background of high alkalinity and pH levels, calcium carbonate is intensively precipitated in the form of scale (the pipes “overgrow”, a white coating forms on the heating elements). That is why the norms of the Kotlonadzor normalize the value of the hardness index of the water used to feed the boilers (0.05–0.1 mg-eq/l). In many industrial processes, hardness salts can react chemically to form unwanted intermediates.
Health impact
The World Health Organization regulates the values of water hardness in terms of health effects. The materials of the organization say that although a number of statistical studies have revealed an inverse relationship between the hardness of drinking water and diseases of the cardiovascular system, the data obtained are still not enough to determine the causal relationship between these phenomena. Also, there is no evidence that soft water has a negative impact on the balance of trace elements in the human body. A number of studies suggest that human absorption of important minerals from water is extremely low, and he receives most of them from food.
Depending on local conditions, the acceptable hardness for drinking water use may vary somewhat. In some cases, water with hardness above 10 meq/l is acceptable to the consumer. The taste threshold for the calcium ion (in terms of mg-equivalent) is in the range of 2-6 meq/l, depending on the corresponding anion, and the taste threshold for magnesium is even lower. So, water with high hardness can have a bitter taste. And long-term use of hard water (usually accompanied by high total mineralization) leads to problems in the gastrointestinal tract.
but on the other hand
It should also be noted that water with a hardness of less than 2 meq/l has low buffering properties (alkalinity) and, depending on the pH level and some other factors, may have an increased corrosive effect on the surfaces of pipes and heating equipment. Therefore, in some cases, especially when in boiler rooms, it is necessary to additionally carry out a special one, which makes it possible to achieve the optimal ratio between the corrosiveness of water and its hardness.
