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Class 12 Water Resources: cheat sheet
CBSE Social Science. India’s surface water and groundwater, how each sector uses water, polluted rivers, and conserving water through watershed management and rainwater harvesting.
Key ideas
- India has about 2.45% of the world’s area and about 4% of its water; surface water comes from rivers, lakes, ponds and tanks.
- The Ganga, Brahmaputra and Barak cover about a third of the area but hold about 60% of the surface water.
- Agriculture uses most water; industrial and domestic shares will grow with development.
- Over-use of groundwater in Punjab, Haryana, Rajasthan and Tamil Nadu has lowered water tables and raised salinity, fluoride and arsenic in places.
- Rivers are polluted by sewage, industrial effluents and farm run-off, spreading water-borne diseases.
- Watershed management conserves a watershed’s land, water and plants with community help; rainwater harvesting raises groundwater and checks erosion and flooding.
- In Rajasthan, rain is stored in covered underground tanks called kunds or tankas.
Remember
| Water in a year | about 4,000 cubic km from rain; 1,122 cubic km utilisable; 432 cubic km replenishable groundwater |
| Use by agriculture | 89% of surface water, 92% of groundwater (industry 2% and 5%; homes 9% of surface water) |
| A sector’s use | per cent × total used ÷ 100 |
| Per person | water supplied ÷ population (litres per person per day) |
| Tank capacity | length × width × depth (m³); 1 m³ = 1,000 litres |
| Polluted stretches | Yamuna between Delhi and Etawah; Ganga at Kanpur |
Watch out
- Thinking industry is the biggest water user (agriculture is, by far).
- Forgetting to multiply cubic metres by 1,000 to get litres.
- Saying rainwater harvesting raises arsenic or salinity: it dilutes contaminants.
Worked example
Suppose 800 cubic km of surface water is used in a year (89% by agriculture, 2% by industry, 9% by homes) and 500 cubic km of groundwater (92% by agriculture). (a) How much surface water does each sector use, and how much groundwater does agriculture use? (b) Why may agriculture’s share fall in future? (c) Name one way to reduce farm water use.
Working: 89%, 2% and 9% of 800; 92% of 500
Answer: (a) agriculture 712, industry 16, domestic 72 cubic km; groundwater for agriculture 460 cubic km (b) industrial and domestic demand will grow with development (c) e.g. drip or sprinkler irrigation, less water-hungry crops
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