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Hard water

hard water

One of the most common water quality problem is water hardness. Water hardness is the total amount of dissolved alkaline earth metal ions. Elements like calcium Ca 2+ and magnesium Mg 2+ are usually taken into account because they make about 98-99% of all compounds. Water hardness is also affected by metals such as beryllium, strontium and barium that belong to the group of heavy metals.

Water hardness indicators

Numerically water hardness is represented as the sum of calcium and magnesium concentrations. Calcium hardness is high in weakly mineralized waters. As mineralization increases, the content of calcium ions decreases. Usually it does not exceed 1 g/l. The content of magnesium ions in highly mineralized waters can reach several grams and in salty waters even several tens of grams.

Water hardness indicators

Group Hardness, mmol/l
Very soft Up to 1.5
Soft From 1.4 to 4.0
Medium hardness From 4.0 to 8.0
Solid From 8.0 to 12.0
Very solid More than 12.0

Types of hardness

Hard water

  1. Temporary or carbonate hardness consists of calcium/magnesium carbonates and bicarbonates Ca(HCO3)2,  Mg(HCO3)2.The hardness can be removed by boiling. The higher the temperature, the lower the solubility. As the temperature rises, deposits occur and limestone deposits forms.
  2. Permanent or non-carbonate hardness is formed by sulfates and chlorides of alkaline earth metals, including CaSO4, CaCl2, MgSO4 un MgCl2. Such water does not form deposits, however, it is important for various technological operations.

Hard water sources

The main source of calcium and magnesium ions are natural minerals: dolomite, calcite, wollastonite, etc. All natural water contains hardness salts, which are formed when water moves through the layers of the earth. In addition, there are also anthropogenic factors that affect water hardness  such as chemical industry wastewater, amber mining, etc.

How to determine water hardness at home?

Very hard water has a bitter aftertaste. It is quite difficult to feel the bitter taste of the water with medium hardness. On the other hand, soft water with low salinity will taste fresh.

In order to accurately determine water hardness it is necessary to conduct water analyzes in a specialized laboratory. Analyzes are recommended if you plan to install a water filter or use the water in the preparation or production of beverages/food products.

Test strips for determining water hardness can also be purchased in specialized stores.

Hard water consumption

Calcium and magnesium are important trace elements of the body. They participate in the work of the heart, blood vessel and urinary systems as well as in the formation of enzymes and bone tissue. There is no organ in the human body in which these chemical elements are not involved.

It is important to remember that both the lack of hardness salts and their excess are equally dangerous. If the water is poorly mineralized, the body tries to compensate the deficit with food. If the water has increased hardness, the urinary system is overloaded and it can form kidney stones, hypertension and edema. Highly mineralized water also contributes to hair dryness and pale shade. This problem can be solved by using special chelating shampoos or filtered water.

Hard water use in the household

Deposits on the heating elements of heating boilers and washing machines are the most frequent reason for their unplanned maintenance. In addition, scale on pipes and heating elements of heating systems significantly reduces the energy efficiency of these devices. Long-term use of hard water can reduce efficiency by up to 30 – 40%,  increasing electricity consumption and electricity bills.

Hard water use in the industry

In some industries water hardness is strictly regulated. Limestone is dangerous for water heating and steam boilers as it reduces the life of the equipment and increases energy costs. In this case the recommended water hardness is  0.02 mmol/l. Strict standards are also applied to the water of the heat exchangers because the reduction of the diameter of the pipes and the excess of thermal conductivity due to the scale layer are dangerous. Water quality is also important in the food industry and beverage production. The optimal parameters for beverage production are 0.2 – 1 mg-equiv/l.

Hard water softening methods

Ciets ūdens

1. Addition of reagents

Using this method, the hardness salts are converted into an insoluble form. For this purpose soda ash Na2CO3, slaked lime Ca(OH)2 or sodium orthophosphate Na3PO4  are usually used. The disadvantage of this method is the damage to the environment since phosphates are not removed in biological treatment plants and end up in the water.

2. Ion exchange

The filtering material of this method is polymer granules which, in contact with water, exchange hardness cations for safe sodium or hydrogen ions. Nowdays, the ion exchange method is often used both for household and industrial purposes.

3. Reverse osmosis

The pores of the reverse osmosis filter membrane have a small size and are able to retain up to 99.8% of mineral impurities. The method is suitable for domestic drinking water or industrial preparation of process water.

Read also: Water softening and de-ironing.

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