You might have observed that in some places tap water lathers easily with soap, while in other places the same amount of soap gives a scum (a curd-like dirty white substance) and hardly any lather.

The water, which does not lather with soap, is called hard water. Dissolved salts of calcium and magnesium make the water hard. Soft water is a comparatively purer form of water. It is tasteless and lathers easily with soap. Distilled water is soft water.

Types of Hardness of Water

Temporary hardness:

Hardness of water caused by the bicarbonates of calcium and magnesium is called temporary hardness. It can be removed by boiling the water. When water is boiled, the bicarbonates of calcium and magnesium decompose to form carbonates. These are insoluble and collect on the sides of the vessel as fur or scale. When calcium and magnesium bicarbonates are removed from the water, it becomes soft.


Permanent hardness:

Hardness caused by the sulphates and chlorides of calcium and magnesium is called permanent hardness, because it cannot be removed by boiling. To remove permanent hardness we have to resort to other methods such as treating the water with sodium carbonate or by passing hard water through ion exchangers, (you shall study about these in higher classes). Distilling the water removes both types of hardness. Distilled water is the purest form of water and the most expensive one!

Disadvantages of Hard Water:

1. It is very difficult to wash clothes with hard water as it requires more soap and leaves a messy scum that cannot be washed out easily.


When hard water is boiled at home or in industries, it leaves deposits of calcium and magnesium salts in kettles, hot-water pipes, boilers and radiators. These deposits reduce the efficiency of boilers, kettles and pipes and can cause blockages and even bursting of the boilers.

Uses of Water

  • Water is vital for life. Humans, plants and animals cannot survive without water.
  • It is required for irrigating crops, as seeds cannot germinate without water.
  • Water is used in cooking and washing. Running water is used to generate electricity.
  • Water serves as a medium for transportation, as ships and boats move on water.
  • Many industries such as petroleum, fertilizer, dye and drugs industries require large quantities of water for various processes.
  • Water is a universal solvent as many substances dissolve in it.
  • Fish, other animals and many plants live in water. Fishing and other water-related activities are a source of livelihood for many people.