📖 PART 1: Sources of Water
Surface Water
- Rivers: Major source of freshwater. Rivers from the Himalayas (Ganga, Yamuna, Indus
system, Brahmaputra) are perennial (flow throughout the year — fed by glaciers + monsoon).
Peninsular rivers (Godavari, Krishna, Kaveri, Mahanadi) are seasonal (mainly monsoon-fed).
- Lakes: Natural freshwater bodies — Wular (J&K largest), Dal Lake (J&K), Pangong
Tso (Ladakh — saltwater). Artificial: reservoirs created by dams.
- Reservoirs (Artificial Lakes): Formed by constructing dams across rivers — store
monsoon water for dry season use.
- Tanks: Traditional tank irrigation — common in Tamil Nadu, Andhra Pradesh, Telangana.
Small ponds/reservoirs built to harvest rainwater for irrigation.
Ground Water
- Water that percolates through soil and rocks and gets stored underground in aquifers.
- Extracted using wells (open dug wells), tube wells (deep borewells),
and artesian wells (confined aquifers where water rises naturally under pressure).
- India is the world's largest user of groundwater — severe depletion in Punjab, Haryana, Rajasthan, and
parts of Tamil Nadu.
🚰 PART 2: Need for Conservation of Water
- India has only 4% of world's freshwater but 18% of world's population.
- Reasons for water scarcity: uneven rainfall distribution, rapid population growth, industrial and
agricultural demand, pollution of rivers and groundwater, overexploitation of groundwater.
- Water is essential for: drinking, irrigation (accounts for ~78% of India's total water use), industry,
hydroelectric power.
🌧️ PART 3: Rain Water Harvesting
Rainwater Harvesting is the collection and storage of rainwater that runs off from
rooftops, land surfaces, or road surfaces — for direct use or for recharging groundwater. It is a
traditional practice revived as a modern conservation method.
Methods and Importance
- Rooftop RWH: Rainwater from rooftops collected via pipes into underground tanks or used
to recharge borewells. Widely practised in cities (Tamil Nadu made it mandatory in Chennai in 2003).
- Surface Runoff RWH: Check dams, ponds, and tanks collect runoff to recharge
groundwater.
- Importance: Reduces dependency on groundwater; recharges aquifers; reduces flooding;
provides self-sufficiency in water even in low-rainfall areas.
- Traditional systems: Johads (Rajasthan — community ponds),
Baolis/stepwells (Gujarat/Rajasthan), Pyne (Bihar), Surangam (Kerala
underground channel), Ahar-Pyne (Bihar irrigation system).
🌾 PART 4: Irrigation — Importance and Methods
Irrigation is the artificial supply of water to agricultural land to supplement rainfall,
especially during dry periods or for crops that need more water than the monsoon provides.
Importance of Irrigation in India
- India's monsoon is unreliable — seasonal and unevenly distributed.
- Rabi crops (wheat, gram, mustard) need water in winter when there is little rainfall.
- Irrigation enables multi-cropping (two or three crops per year) and area expansion.
- Essential for Green Revolution (HYV seeds need controlled water supply).
Methods of Irrigation
| Method |
How it Works |
Advantages |
Disadvantages / Use |
| Wells (Open Dug Wells) |
Shallow, manually dug wells; farmers lower buckets or use Persian wheel (rehat) to draw water
|
Inexpensive; decentralised; good for small farms |
Limited to shallow water table; labour-intensive |
| Tube Wells |
Deep borewells fitted with pumps (diesel or electric); draw water from deep aquifers |
Large volumes; available year-round |
High energy cost; depletes groundwater rapidly; common in Punjab, UP, Haryana |
| Tanks |
Rainwater and runoff stored in earthen embankments; water released to fields by channels |
Traditional; low cost; recharges groundwater |
Seasonal; dependent on rainfall; siltation problem over time. Common in Tamil Nadu, Andhra,
Telangana |
| Canal Irrigation |
Water diverted from rivers into a network of main canals, branch canals, and distributaries |
Large-scale; perennial (from river); reduces dependence on rainfall |
Waterlogging and soil salinity if poorly managed; high capital cost. Common in Punjab, Haryana,
UP, Rajasthan (Indira Gandhi Canal) |
| Drip Irrigation |
Water delivered directly to plant roots via a network of pipes and emitters — drop by drop |
Highly water-efficient (up to 50–70% water saving); ideal for orchards, vegetables,
horticultural crops |
High initial cost; clogging issues; not suitable for field crops. Promoted by Israel-India
cooperation; widely used in Maharashtra, Rajasthan |
| Sprinkler Irrigation |
Pressurised water sprayed over fields through rotating sprinklers — simulates rainfall |
Efficient; good for uneven terrain; reduces soil erosion; used for lawns, tea, vegetables |
Wind can affect distribution; energy required; not ideal for tall crops |
📝 Quick Revision – Key Facts
| Topic |
Key Fact |
| Largest freshwater lake (India) |
Wular Lake (J&K) |
| India's water use |
~78% for agriculture (irrigation) |
| RWH mandatory city |
Chennai (Tamil Nadu) — since 2003 |
| Johad |
Traditional community ponds — Rajasthan |
| Most water-efficient irrigation |
Drip Irrigation |
| Canal irrigation belt |
Punjab, Haryana, UP (Ganga-Yamuna Doab); Rajasthan (Indira Gandhi Canal) |
| Tank irrigation |
Tamil Nadu, Andhra Pradesh, Telangana |
📌 Chapter Summary
- Surface water: rivers (perennial Himalayan; seasonal Peninsular), lakes, reservoirs, tanks. Ground
water: wells, tube wells, artesian wells.
- Water conservation needed — India has 4% of world's freshwater but 18% of its population.
- Rainwater Harvesting: rooftop and surface runoff collection; traditional johads, baolis, tank
systems.
- Irrigation methods: Wells (small scale), Tube wells (depletes groundwater fast), Tanks (S. India),
Canals (Punjab/Rajasthan), Drip (most efficient — orchards), Sprinkler (uneven terrain).