Chapter 3: Water Resources | Summary

Dams were traditionally built to impound rivers and rainwater for irrigation. Today, dams serve multiple purposes: electricity generation, domestic and industrial water supply, flood control, recreation, inland navigation, and fish breeding. They are therefore referred to as multi-purpose projects. The Bhakra-Nangal project on the Sutluj-Beas river basin is used for both hydel power and irrigation, while the Hirakud project on the Mahanadi integrates water conservation with flood control.

After Independence, multi-purpose projects were envisioned as engines of national development. Jawaharlal Nehru called dams the 'temples of modern India', believing they would integrate agricultural and industrial development. The Sardar Sarovar Dam on the Narmada River is one of the largest such projects, covering four states — Maharashtra, Madhya Pradesh, Gujarat, and Rajasthan — and providing irrigation to 18.45 lakh hectares of land.

Multi-purpose projects have come under severe criticism in recent years. Regulating and damming rivers affects their natural flow, causing poor sediment flow and excessive sedimentation at the reservoir bottom, resulting in rockier stream beds and poorer aquatic habitats. Dams fragment rivers, making it difficult for aquatic fauna to migrate for spawning. Reservoirs submerge existing vegetation and soil, leading to decomposition over time.

The dams designed to control floods have paradoxically triggered floods due to reservoir sedimentation. Flood plains are deprived of silt — a natural fertiliser — causing land degradation. Multi-purpose projects have also been linked to induced earthquakes, water-borne diseases, and pollution from excessive water use. Irrigation from these projects has changed cropping patterns, with farmers shifting to water-intensive crops, leading to ecological consequences like salinisation of soil.

India has an ancient and extraordinary tradition of water harvesting. People had in-depth knowledge of rainfall regimes and soil types and developed diverse techniques suited to local ecological conditions. In hill and mountainous regions, diversion channels called 'guls' or 'kuls' were built in the Western Himalayas. In Bengal's flood plains, inundation channels were developed to irrigate fields. In arid and semi-arid regions, 'khadins' in Jaisalmer and 'johads' in other parts of Rajasthan converted agricultural fields into rain-fed storage structures.

In semi-arid Rajasthan — particularly in Bikaner, Phalodi, and Barmer — almost all houses traditionally had underground tanks called 'tankas' for storing drinking water. Rainwater, known locally as 'palar pani', was considered the purest form of natural water. The tankas were connected to sloping roofs through pipes, and the first spell of rain was not collected so as to clean the roofs and pipes before storage began.

Rooftop rainwater harvesting is being successfully adapted across rural and urban India. Tamil Nadu is the first state to make rooftop rainwater harvesting compulsory for all houses, with legal provisions to penalise defaulters. In Shillong, Meghalaya, nearly every household has a rooftop rainwater harvesting structure, supplying 15–25 percent of total household water needs. In Gendathur village, Karnataka, about 200 households have installed this system, collectively harvesting 1,00,000 litres of water annually.

Meghalaya also has a 200-year-old tradition of tapping stream and spring water using bamboo pipes, transporting water over hundreds of metres. In western Rajasthan, the practice of rooftop harvesting has declined due to water availability from the Indira Gandhi Canal, though some households retain their tankas due to preference for the taste of harvested rainwater. Government schemes like Jal Jeevan Mission (JJM) and Atal Bhujal Yojana have been launched to ensure assured piped water supply and promote community-based water conservation.

Water Resources is a chapter that highlights the paradox of water abundance and scarcity. Though water is a renewable resource, over-exploitation, pollution, unequal distribution, and rapid population growth have made water scarcity a pressing global challenge. Multi-purpose river projects offered a modern solution but have been accompanied by significant ecological, social, and geological drawbacks. Traditional water harvesting methods, practised across India for centuries, offer a viable, environmentally sound alternative that needs to be revived and adapted.

From a board examination perspective, this chapter is highly significant. Students must understand the causes of water scarcity, the advantages and disadvantages of multi-purpose projects, traditional harvesting systems region-by-region (guls, khadins, johads, tankas, bamboo pipes), and key government schemes like Jal Jeevan Mission and Atal Bhujal Yojana. Map-based questions on major dams and rivers, case studies of Bhakra-Nangal and Hirakud, and critical analysis of large dam impacts are frequently tested in CBSE board exams.