Geography · Ch 12 — Water Resources
Deterioration of Water Quality
Deterioration of Water Quality
Water quality means the purity of water — water that is free from unwanted foreign substances. When foreign matter such as micro-organisms, chemicals, industrial waste, and other wastes enter water bodies, the quality deteriorates and the water becomes unfit for human use. Toxic substances that enter lakes, streams, rivers, and oceans either dissolve or remain suspended in the water. This causes water pollution, which harms aquatic systems. Sometimes these pollutants also seep into the ground and pollute groundwater.
Sources of water pollution
The major rivers of India retain better water quality in their upper, less densely populated stretches in hilly areas. In the plains, river water is used intensively for irrigation, drinking, domestic purposes, and industry. Drains carrying agricultural runoff (fertilisers and insecticides), domestic waste (solid and liquid), and industrial effluents all join the rivers. The concentration of pollutants in rivers is especially high during the summer season, when the flow of water is low.
The Central Pollution Control Board (CPCB), in collaboration with State Pollution Control Boards, monitors water quality at 507 stations across the country. Data from these stations show that organic and bacterial contamination remains the main source of pollution in rivers.
Most polluted rivers and stretches
- The Yamuna river is the most polluted river in the country, especially between Delhi and Etawah.
- Other severely polluted rivers include:
- Sabarmati at Ahmedabad
- Gomti at Lucknow
- Kali, Adyar, and Cooum (entire stretches)
- Vaigai at Madurai
- Musi at Hyderabad
- Ganga at Kanpur and Varanasi
Groundwater pollution
Groundwater pollution has occurred due to high concentrations of heavy or toxic metals, fluoride, and nitrates in different parts of the country. Over-withdrawal of groundwater in states like Rajasthan and Maharashtra has increased fluoride concentration. In parts of West Bengal and Bihar, overuse has led to increased arsenic concentration in groundwater.
Legislative measures and their effectiveness
The Water (Prevention and Control of Pollution) Act, 1974, and the Environment Protection Act, 1986, were enacted to control water pollution. However, these laws have not been implemented effectively. As a result, in 1997, as many as 251 polluting industries were located along rivers and lakes. The Water Cess Act, 1977, which was meant to reduce pollution, has also had only marginal impact.
There is a strong need to generate public awareness about the importance of water and the impacts of water pollution. Public awareness and action can be very effective in reducing pollutants from agricultural activities, domestic sources, and industrial discharges.
Recycle and reuse of water …
The map is a schematic outline of India showing the full course of the Ganga River and its major tributaries, especially the Yamuna. It is not drawn to scale but includes a graticule (latitude-longitude grid) and a north arrow for orientation. A scale bar from 0 to 600 km is provided.
Three towns are explicitly labelled: Delhi (on the Yamuna), Prayagraj (at the confluence of the Ganga and Yamuna), and Varanasi (on the Ganga). A legend distinguishes two types of settlements: a large dot for 'CITY OF VARANASI' and a small dot for 'OTHER BIG CITIES'. The map also carries a legend headed 'AREA OF IRRIGATED LAND', though the description does not specify how this area is shown — it likely uses a shading or pattern to indicate irrigated tracts along the river plains.
Three callout labels with arrows mark water quality along the river system:
- 'Good Quality Water here' — placed on the upper Ganga in the hilly region (the Himalayan stretch).
- 'Poor Quality Water here' — placed near Delhi on the Yamuna River.
- 'Poor Quality Water here' — placed on the lower Ganga stretch near the Bangladesh border.
The map directly illustrates the textbook's point that rivers retain better water quality in less densely populated upper stretches, but deteriorate sharply as they flow through urban and industrial centres. The Yamuna near Delhi and the lower Ganga near the delta are shown as zones of poor quality — matching the text's mention of the Yamuna as the most polluted river between Delhi and Etawah, and the Ganga at Kanpur and Varanasi. …