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Determination of hardness of water by EDTA method

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Determination of hardness of water by EDTA method is one of the three main methods for determination of hardness of water. EDTA means Ethylenediaminetetraacetic acid. This EDTA reagent can be forming edta-metal complexes by the reaction with metal ions except for alkali metal ions. This reagent can forms a stable complex with the alkaline earth metal like calcium ion and magnesium ion in alkaline condition pH above 9.0. Therefore the total hardness of water can be determination by edta titration method.

In this method buffer solution is used for attain suitable condition i.e pH level above 9 for the titration. Buffer solution preserve pH at a balanced position. In aqueous solution edta exist as H2Y2- form. Hence edta react with alkaline earth metals as 1:1. As a result for every mole of alkaline earth metal ion in water sample, one mole of EDTA will be consumed during titration.

Reaction: H2Y2- + M2+ → MY2- + 2H+

During titration Eriochrome Black T is used as indicator. The indicator is red in color when it is forms complexes with the metal ions and blue in color when it is free.

Reaction: MIn– + H2Y2- → HIn2- + MY2- + H+

Determination of hardness of water by EDTA method is father classified into four methods.
Determination of hardness of water-1971

  • Ammonia Buffer procedure
  • Borate Buffer procedure
  • Low hardness procedure
  • Calcium hardness procedure.

Ammonia Buffer procedure: This type determination of hardness of water by EDTA method is especially preferred for those water, where is unfamiliar composition, sewage water, alkalinity or acidity high and for industrial waste water. This method can also be used for normal water. A high capability buffer solution is used to conquer buffering substance in the sample. It has mainly three disadvantages;

  • Utilize of ammonia buffer solution may perhaps not be acceptable if Nessler ammonia determination are being carried out in the same room.
  • If the water sample contains high in calcium ion and bicarbonate ion, it is a affinity for calcium carbonate to be precipitated.
  • The existence of magnesium in the titrant.

Borate Buffer procedure: Borate buffer method is a simpler among the determination of hardness of water by EDTA method. This method is to overcome the limitation of ammonia buffer method. This method does not liberate any ammonia; somewhat calcium carbonate precipitated but not totally holds back. It is not suitable for those water; which is unfamiliar water sample, contains acidity or high alkalinity, industrial waste and sewage.

Low hardness procedure: This is another type of determination of hardness of water by EDTA method. This method is used for waters of low hardness less than 5 mg/l and also for ionexchange effluent or other conditioning water.


Calcium hardness procedure: This method is used for determination of calcium hardness, but it is not standard accurate method for calcium.

Determination of Water Hardness

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Theoretically water hardness means the concentrations of all the metallic cations except the cations of the alkali metals. All nonmetallic ions like Hydrogen ion are excluded from the definition. Normally in the largest part waters, all off the water hardness is occurred by reason of the presence of calcium and magnesium ions. But in some water it should be consideration the measurable concentration of iron, zinc, manganese, aluminum, strontium and other metals. The water hardness is expressed as equivalent concentration of calcium carbonate.





There are different methods for determination of water hardness; following three methods are major:

(i) Hardness by calculation,

(ii) Soap titration method and

(iii) Compleximetric or EDTA titration method.

Hardness by calculation

Hardness by calculation is taking into consideration the most accurate method for determination of water hardness. This method is appropriate to all waters. In this method at first we have to analysis the concentration of calcium and magnesium cations. Then we have to analysis the other hardness producing cations, if their amount is significant. After that the total result is express as equivalent calcium carbonate concentration.

To obtain equivalent calcium carbonate concentration, it should be multiple the concentration of each water hardness producing cations separately by the proper factor. By together all the consequence we get our final result of sample water. Following are the proper factor for determination of water hardness for different cations.

Ca2+ (mg/l) × 2.497

Mg2+ (mg/l) × 4.116

Fe2+ (mg/l) × 1.792

Zn2+ (mg/l) × 1.531

Mn2+ (mg/l) × 1.822

Al3+ (mg/l) × 5.567

Soap titration Method

All water hardness should not be calculated by the soap titration method such as brines, water hardness over 140 mg/l (required dilution). But it is applicable approximately all water. In this process the determination of water hardness definite by the capacity of soap consuming of the water. The precision and accuracy of determination of water hardness by this process may be variation upon people to people and  the skill and experience of the analyst. Moreover Magnesium hardness is less accurate.

The result is interference by some parameter. Temperature is one of the interfering parameter. It is effects of lather factor and standardization factor. The presences of foam breakers or foaming substances also interfere on the titration result. It is one of the oldest methods for determination of water hardness.

Complexeximetric or EDTA titration method

EDTA titration method for determination of water hardness can also be classified into following method:

Ammonia Buffer procedure

Borate Buffer procedure

Low hardness procedure

Calcium hardness procedure.

Industrial effects of Hard Water

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Hard water effects significantly in industries. It can be said that in every industrial purpose it should be use conditioning water rather than hard water. Such as Beverages, textile industries, boiler, cooling tower and plumbing purposes.

Effect of Hard Water in Textile Industry

Water hardness greatly effects on textile dyeing, washing and finishing section. In washing section hard water make the yarn stiff and scratchy. Hard water contains tiny mineral particles and these particles mix with soap turn into like small pieces of rock. Iron containing hard water creates reddish yellow color on washed fabrics. Imperfect soil removal from fabric lessens the colors intensity; an unpleasant odor may be developed. Insoluble soap scum and dirt on the fabrics or yarn lead to yellowish color and uneven dying.

Effects of hard water in beverage industries

Water uses in beverages industries is very sensitive. Water should be free from any contaminants and microorganisms. If hard water used in these industries, it can be change the soft drinks color, test and odor. Moreover a deposit can be developed here. So water must be conditioning before uses for decreasing the effects of hard water in beverages industries. Otherwise lessen the product quality.

Plumbing effects of hard water and repair

Hard water creates a plumbing problem. It can be reduced the life of plumbing and needs more repairs time. Calcium and magnesium ions present in hard water and these ions can be made lime scale. This lime scale can be accumulated some water flow restricted point like pipe bending point, Shower heads, faucet and valves. It reduces flow through the pipes. Sooner or later pipes can turn into completely clogged. Consequently, it increase downtimes for plumbing repair or sometimes may be required pipe replacement.

Effects on cooling towers

In cooling towers water is used as heat transfer medium. If hard water is used in this case, it makes scale, corrosion in cooling towers. Dissolved iron in hard water precipitate in cooling towers basin and also corrosive. Calcium and magnesium developed scale. This scale reduces water flow, heat transfer and makes temperature drops. Hence increase the repair cost.

In hard water different ions are present. When two different type of metal are present in the medium of hard water; these ions can be act as an electrolyte. As a result it leads to corrosion.

In boiler heat is applied to steam formation. When hard water is used in boiler hard crystalline deposits of calcium carbonate, calcium sulfate, magnesium carbonate are formed. This insoluble solid is mainly caused by thermal decomposition of bicarbonate ions from temporary hardness. The resultant lime scale reduced the heating efficiency. Hence it is need further heating; also overheat the metal boiler. This overheating can lead to damage the boiler. In pipe line this scale also restricts the water flow.

industrial water
Industrial Water Quality

Whole house hold effects of hard water

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There are several negative effects of hard water in whole house hold work such as limescale form in coffee makers, tea kettles, hot water heaters, steam irons, washing machine, faucets, shower heads, inside of pipes, taps etc. More soap and detergent is required in washing purpose.

When limescale are formed inside of pipes; it decreases flow through the pipes. In the long run pipes can turn into completely clogged. As a result sometimes may be required pipe replacement.

When hot water heater is heated with presence of hard water a scale is formed. This scale reduced the heating efficiency. Hence increase the heating cost.

When hard water is used in tea maker kettles or coffee makers as like hot water heater, a lime scale (insoluble calcium carbonate or calcium sulfate) can be developed insides of its. Moreover, the mineral presence in hard water can also be creating bitter test. In addition a film can observe on tea or coffee.

Ca2+(aq) + CO32-(aq) = CaCO3(s)

Soap is a sodium or potassium salt of fatty acid. When soap is added in hard water a white deposit is formed which is call soap scum. In this case the calcium and magnesium ions of hard water react with soap and replace the sodium or potassium ions and create another salt which is called lime soap.

2 C17H35COO– + Ca2+ → (C17H35COO)2Ca

This lime soap is preventing to producing lather of soap and ineffective in washing purpose. Synthetic detergent is less vulnerable than soap in hard water. Scum is not formed by detergents. The reason for in synthetic detergents the active in gradient is sulphate or sulphonates which is inactivated to hardness.

In laundry purpose hard water can effects on fabric. It makes the yarn stiff and scratchy. Imperfect soil elimination from fabric lessens the colors intensity; an unpleasant odor may be developed. Moreover continuous washing in hard water can damage fibers and decrease the fabric life. If iron exists in hard water as ferric form a reddish yellow color can be developed on washed clothes. In addition it can make deposits in plumbing fixtures.

Hard Water Effects on Health

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Hard water has no recognized undesirable effects on health; On the other hand, a small amount of calcium and magnesium mineral is daily need for our health. Some people are advice by their physician to use hard water for drinking and cooking. A under investigated studies has been shows that drinking hard water can reduce heart attack risks. Extremely rare cases, where calcium concentrations are bigger than 1000 mg/L in hard water can be enlarged occurrence of kidney stones and gallstones.

Using hard water some people observe additional dry skin, but the greater part of people are not seen any change.

Another survey has been shown that when some people with Eczema started to using soft water their skin improves. The cause is unknown why the skin improves? This effects on health may be caused by the calcium and magnesium salt on hard water. In hard water when people bathing with soap, a sticky film formed on the skin. Soil, dirt and bacteria can be trapped in pores beneath the soap scum; this is the possible skin infection.
The soap scum stick in hair. As a result hair can be dull, limp and complicated to handle. Moreover this scum can be reason for hair fallen.

Some research have shows that a correlation between hard water and cardiovascular disease. Hard water enhances the some vital minerals like calcium and magnesium. These two minerals may possibly have a defensive effect in opposition to cardiovascular disease and diminish threat of high blood pressure. World Health Organization analysis the data but the data was not enough to permit for a suggestion of a level of water hardness.

Thought hard water has some negative effects on health, but in broad-spectrum it is beneficial to health.

Effects of hard water

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There are many negative and positive effects of hard water. But actually negative effects are dominants. Mainly we observe the following effects of hard water.

Whole house hold effects of hard water

In whole house hold work hard water can form limescale in kettles, coffee makers, faucets, hot water heaters, steam irons, automatic dishwashers, shower heads, inside of pipes, taps etc. When hard water is used for washing more soap or detergents are required. Moreover hard water leaves soap or detergent deposits in sinks, bathtubs and basins; create spots on glassware and dishes.

Effects of hard water on health

There are no significant effects of hard water on health. Moreover a little amount of calcium and magnesium mineral is good for our health. Though it has some effects on skin and hair, but it reduce heart attack risks.

Industrial effects of hard water

Mainly effects of hard water are greatly observed in industries.  When hard water is heated a lime scale is formed inside of pipes, hot water tanks, washing machines, boilers, cooling towers and other industrial equipment that handles water. It can be reduced the life of plumbing. Water hardness significantly effects on textile dyeing, washing and finishing section. Hence water must be conditioning before industrial uses.

Sources of Water

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There are different sources of water. About 75 percent of the earth’s surface is covered with water. But all water is not suitable for drinking. It should be conditioning before use. Water is essential for every living thing on the earth. The sources of water mainly classified into four groups.

Surface Water:

Surface water means the water that are present on the surface of the earth. The main sources of surface water are rain and snow. This class of water further can be divided in to two classes’ static and moving surface water. River, streams and canal water are moving surface water; on the other hand lake and ponds water are static surface water. Sea water is not included into surface water. Surface water is contaminant with turbidity, suspended solids, micro-organism, bacteria, Ca and Mg salt, bad order, taste and color.

Ground Water:

Part of the rainwater falls on earth soaks through the soil. This water stock up in the ground as soil moisture. The ground water are spring water, sinking tube wells. There are no turbidity, microbial in ground water. But it is contaminants by higher hardness, dissolved gasses.

Rain Water:

When atmospheric water vapor precipitates and become heavy enough to fall earth as droplet is called rain water.  Rain water is weakly acidic because it is absorbs carbon-di-oxide. Industrial uses of this water is little amount.

Sea water

Sea water has salinity. The use of this water is limited. It is very hard to treatments. Oxygen and carbon di-oxide also dissolved in it.