Water Resources — Notes

Water covers about three-quarters of Earth's surface, but about 96.5 per cent of it is in the oceans. Only about 2.5 per cent is fresh water; roughly 70 per cent of that is frozen in ice sheets and glaciers (Antarctica, Greenland, high mountains) and nearly all the rest is groundwater. Rivers and lakes hold a tiny share.

Fresh water is renewable because the hydrological cycle (evaporation, condensation, precipitation, runoff and infiltration) keeps refilling rivers and aquifers. Renewable is not the same as unlimited: if we pump or pollute faster than the cycle refills, water runs short.

India receives about 4 per cent of the world's precipitation, but most of it falls in the monsoon months and it is spread very unevenly across regions.

Water scarcity means not having enough water of usable quality for people's needs. In India it is caused less by a lack of rain than by how water is used:

• Over-exploitation: tube wells and borewells pump groundwater faster than rain recharges it, so water tables fall.
• Excessive use: irrigated agriculture is the largest user; dry-season (rabi) cropping and water-hungry crops raise demand.
• Growing population: more water for homes and more food to grow.
• Urbanisation and industry: crowded cities and water-intensive lifestyles; many housing societies and industries pump their own groundwater; industries also need power, part of it from hydroelectric plants.
• Unequal access: richer groups may have deep borewells while poorer ones depend on tankers.
• Bad quality: sewage, industrial waste, pesticides and fertilisers make water unfit to use even where it is plentiful.

Why conserve? To keep people safe from water-borne illness, to secure food supplies, to keep farms, factories and other work running, and to keep rivers, wetlands and other ecosystems healthy. Over-use and mismanagement can lead to an ecological crisis.

Old traditions. Indians built stone-rubble dams, reservoirs, embankments and canals long ago:

• Sringaverapura near Prayagraj: a system harvesting the Ganga's floodwater, about the first century BCE.
• Under Chandragupta Maurya, dams, lakes and irrigation works were built widely.
• Ancient irrigation works at Kalinga (Odisha), Nagarjunakonda (Andhra Pradesh), Bennur (Karnataka) and Kolhapur (Maharashtra).
• The great lake at Bhopal (eleventh century) was among the largest artificial lakes of its time.

Dams. A dam is a wall built across a river or stream to control how its water flows; the water held back forms a reservoir. Dams are classified by structure and material (timber, embankment, masonry) and by height.

Multi-purpose projects serve irrigation, hydroelectricity, domestic and industrial water supply, flood control, recreation, inland navigation and fish breeding at once. Examples: Bhakra Nangal (Sutlej–Beas basin) for power and irrigation; Hirakud (Mahanadi) combining water conservation with flood control; Sardar Sarovar (Narmada, Gujarat) serving Gujarat, Maharashtra, Madhya Pradesh and Rajasthan, especially drought-prone areas. Jawaharlal Nehru called dams the "temples of modern India", expecting them to drive progress on farms and in villages and in factories and cities at the same time.

Environmental costs. Dams change a river's natural flow: sediment settles in the reservoir, so the riverbed below turns stony and offers less food and shelter to aquatic life; rivers are fragmented, so fish cannot migrate to spawn; floodplain vegetation and soil are submerged and decompose. Floodplains lose silt, their natural fertiliser. Projects have also been linked to induced earthquakes, water-borne diseases and pests.

Social costs. Large-scale displacement of local communities, who often lose land and livelihoods and gain little; benefits go largely to landowners, large farmers, industrialists and some cities. Irrigation shifts farmers to water-intensive commercial crops, causing salinisation and widening the gap between rich landowners and the landless poor.

Conflicts. Between users (farmers in the Sabarmati basin of Gujarat protested when urban supply got priority in a drought) and between states (Karnataka and Andhra Pradesh objected to Maharashtra diverting more water at Koyna in the Krishna basin). Some flood-control dams have worsened floods because of sedimentation and large releases in heavy rain (Maharashtra and Gujarat, 2006).

Movements: the Narmada Bachao Andolan (adivasi communities, farmers, environmental groups and rights activists) opposed the Sardar Sarovar Dam, first over submergence and later over rehabilitation of the displaced; there was also a movement against the Tehri dam.

Board map list (locate and label): Salal (Chenab, J&K), Bhakra Nangal (Sutlej, Himachal Pradesh–Punjab), Tehri (Bhagirathi, Uttarakhand), Rana Pratap Sagar (Chambal, Rajasthan), Sardar Sarovar (Narmada, Gujarat), Hirakud (Mahanadi, Odisha), Nagarjuna Sagar (Krishna, Telangana–Andhra Pradesh border), Tungabhadra (Tungabhadra, Karnataka).

Because of the costs of large dams, many see rainwater harvesting as a socially, economically and environmentally viable alternative: it is cheap, local, run by communities, causes no displacement and recharges groundwater.

Traditional methods

• Guls or kuls — diversion channels in the western Himalayas carrying stream water to fields.
• Rooftop harvesting — common in Rajasthan for drinking water.
• Inundation channels — in the floodplains of Bengal, leading floodwater to fields.
• Khadins (Jaisalmer) and johads (other parts of Rajasthan) — fields ringed by earthen embankments that trap runoff, keeping the ground moist enough to sow a crop.
• Tankas — underground tanks in houses of Bikaner, Phalodi and Barmer, linked to the sloping roof by a pipe. The first rain is let out to clean the roof and pipes. Stored rain, palar pani, is valued as the purest water. Rooms beside the tanka stay cool. The practice has declined where the perennial Indira Gandhi Canal now supplies water, though some families keep tankas because they prefer the taste of rainwater.
• Bamboo drip irrigation — a Meghalaya practice about 200 years old: bamboo pipes carry stream or spring water downhill and the flow is reduced until it reaches plants drop by drop.

Today: Tamil Nadu was the first state to make rooftop rainwater harvesting structures compulsory for all houses, backed by penalties. In Shillong, near some of the rainiest places on Earth, many households still harvest roof water to meet part of their needs. Villages in Karnataka have shown that household rooftop systems can make a village water-secure.