Hardness of Water

The presence of calcium, magnesium salts, i.e.: bi-carbonates, sulphates, chlorides, in water is called hardness of water. The water which contains these salts is called hard water.

Hardness is a term applied to the water denoting a measurement of its pH and metal salts contest.

Classification of Hardness: Hardness is two types. They are:

1. Temporary hardness.
2. Permanent hardness.

Temporary hardness: Temporary hardness is due to the presence of bi-carbonates of calcium and magnesium. This type of hardness is called temporary hardness. It can be removed by easy means like boiling.

Permanent hardness: It is due to the presence of chlorides or sulphates of calcium and magnesium. This type of hardness is called permanent hardness. These salts do not decompose on boiling. So permanent hardness can not be removed.

Method of expressing hardness of water: The hardness of water is expressed by the amount of calcium present in water. In this method chloride, sulphates and bi-carbonates of calcium and magnesium are not takes. Hardness of water is expressed by:

1. PPM (Parts per million).
2. In degrees (Grains/gallon).

PPM: The number of grains of calcium carbonates which is present in one million grains of water is called PPM. 1 grain of calcium carbonate present in 1 million grain water.

In degree: The number of grains of calcium carbonates which is present in 70000 grain of water.