1. Water Quality 1

2. I-The hydrologic cycle (Water Cycle): 2

3. II- Water Resources:- a- Surface water i. Fresh water (Rivers) ii. Brackish water (Lakes) iii. Saline water (Oceans & Seas) b- Underground water (Wells & Springs) 3

4. Water pollution is the presence of any material (contaminant) in water that is harmful to human, animal and plant, or affects its taste or odour. 4

5. Domestic water pollution Industrial water pollution Agricultural water pollution. 5

6. The Quality of water is significant as its Quantity. In fact, more than 97.5 % of earths water is saline, and hence not readily available for use. Water Quality is generally expressed in terms of its Physical, Chemical and Bacteriological characteristics. 6

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8. The change in chemical characteristics of water alter water quality greatly. For example, nitrites and nitrates in water can cause methemoglobinemia, commonly known as blue baby syndrome. 8

9. Bacteria and microorganisms, present in water, are of microscopic size (1 to 4 micron). Harmful bacteria, causing different diseases, are known as pathogenic bacteria, while the harmless ones are known as non-pathogenic bacteria. 9

10. Note The quality and composition of dissolved salts in water depends upon the nature of the rock or soil with which it has come in contact. Thus, ground water has generally a higher salt content as compared to surface water. 10

11. General Standards of Quality of Water for Different Uses The use of water may be grouped into: i. Domestic ii. Irrigational iii. Industrial Each group has its own standards of water quality. 11

12. Domestic Use: Water required for domestic purposes must obviously be colourless, odourless and tasteless. It should be free from turbidity, chemical compounds, harmful micro-organisms and radioactivity. 12

13. Standards for quality of water for domestic use cannot be expressed in absolute values as they vary with variations in human tolerance and adaptability. 13

14. For example, water having more than 500 ppm of dissolved solids in not considered suitable for drinking purposes in most of the humid temperate regions of the world, whereas that with 1500 ppm of dissolved salts is regarded as acceptable for drinking in most of the arid regions. 14