Types of Impurities in Water

Unit - I

Chapter 1

Water and its Treatment

INTRODUCTION

Water is the most important compound for the existence of human beings, animals and plants. About 80% of the earth's surface is occupied by water. The main sources of water are

(i) rain

(ii) rivers and lakes (surface water)

(iii) wells and springs (underground water)

(iv) sea water.

Among the above sources of water, rain water is the purest form of water but it is very difficult to collect whereas sea water is the most impure form. So, surface and underground water are normally used for domestic and industrial purposes. Such water must be free from undesirable impurities. The process of removing all types of impurities from water and making it fit for domestic or industrial purposes is called water treatment. Before treating the water, we should know the nature as well as the amount of impurities.

TYPES OF IMPURITIES IN WATER

The impurities present in the water may be broadly classified into three types.

1. Physical impurities

(a) Suspended impurities like sand, oil droplets, vegetable and animal matter, impart turbidity to water.

(b) Colloidal impurities like finely divided silica, clay and organic waste products impart colour, odour and taste to water.

2. Chemical impurities

(a) Dissolved salts like bicarbonates, sulphates and chlorides of Ca and Mg and carbonates, bicarbonates of Na and K.

Dissolved Mg and Ca salts in water cause "hardness", whereas alkali salts (bicarbonates, carbonates of K and Na and bicarbonates of Ca & Mg) make the water “alkaline".

(b) Dissolved gases like O₂, CO₂, H₂S, SO₂ make the water “acidic". So they accelerate the rate of corrosion.

3. Bacterial impurities like fungi, bacteria and other microorganisms cause diseases.