Water resources of India

Geography glossary

Topic: Water Resources of India: Availability, Use and Conservation · NCERT: Class 12, Ch 4 "Water Resources"

Meaning

Water resources of India are all the water India gets each year from rain and snow (precipitation), plus the water that reaches its rivers, lakes and aquifers. Only part of this water can actually be used. India has about 2.45% of the world's area and about 4% of its water, but over 17% of its people (NCERT; now about 18%). This mismatch is the main cause of India's water stress (when demand for water comes close to, or goes beyond, the supply that can be used).

Explanation

Basic nature of water

  • Water is a cyclic resource. It keeps returning through the hydrological cycle (water cycle).
  • The sun heats seas and land, and water evaporates.
  • The vapour cools and condenses, and falls back as rain or snow (precipitation).

  • The water flows through rivers, lakes and the ground, back to the sea.

  • So water is renewable, because nature refills it. But it still runs short if we use it faster than it is refilled, or if we pollute it.

  • Water is abiotic (not living), like soil, minerals and air.
  • Water covers about 71% of the earth's surface. Only about 3% of all water is freshwater (not salty), and most of that is locked in ice sheets, glaciers and deep groundwater.

From rainfall to usable water: the funnel

  • Step 1: Precipitation (input)
  • NCERT: about 4,000 cubic km a year.

  • CWC 2019 reassessment: mean annual rainfall over India's river basins = 3,880 BCM (1985–2015) [2]. (BCM = billion cubic metres; 1 BCM = 1 cubic km.)

  • Step 2: Total water resource

  • Much rain is lost through evapotranspiration (water that evaporates, plus water that plants release into the air from their leaves).
  • NCERT: surface water + replenishable groundwater (groundwater refilled each year by rain soaking into the ground) = 1,869 cubic km.

  • CWC 2019: average annual water resource = 1,999.20 BCM [2].

  • Step 3: Utilisable water (what we can actually take out with dams, canals and wells)

  • NCERT: only about 60%, which is 1,122 cubic km (690 surface + 432 groundwater).
  • CWC 2019: 1,137 BCM, made up of 690 BCM surface water + 447 BCM groundwater [2].
  • The rest is lost to floods, flows into the sea, or lies where it cannot be stored.
Stage NCERT (older CWC) CWC 2019 [2]
Precipitation ~4,000 km³ 3,880 BCM
Total water resource 1,869 km³ 1,999.20 BCM
Utilisable surface water 690 km³ 690 BCM
Utilisable groundwater 432 km³ 447 BCM
Total utilisable 1,122 km³ 1,137 BCM
  • Key point: usable surface water stayed at 690. The total rose only because the groundwater figure went up (432 → 447) [2].

Surface water and why so little of it is usable

  • Surface water comes from four main sources: rivers, lakes, ponds and tanks. A tank is a small reservoir made by building an earthen bund across a slope or stream. Tanks are common in peninsular India.
  • India has about 10,360 rivers and tributaries longer than 1.6 km. Their mean annual flow is about 1,869 cubic km.
  • Only about 690 cubic km (32%, NCERT) can be used. There are three reasons:
  • Topography: steep Himalayan slopes and narrow gorges make big storage hard, and flat deltas have few good dam sites.
  • Hydrology: much of the flow comes as sudden floods that rush to the sea.

  • Monsoon concentration: most rain falls in about four months (June–September), so dry-season flow is low.

  • What decides a river's flow: the size of its catchment area (all the land that drains into the river) and the rainfall in that catchment. The Brahmaputra has a large catchment and heavy rain, so its flow is large.

Lagoons and backwaters: a brackish endowment

  • A lagoon is shallow coastal water cut off from the sea by a sandbar or spit (a long ridge of sand), but still joined to it by narrow openings.
  • Waves and currents carry sand along the coast.
  • The sand builds bars across bays and river mouths.

  • Water gets trapped behind the bar, and a lagoon forms. This happens on indented coasts (coasts with many inlets and curves).

  • Backwaters are a linked network of lagoons, lakes and canals that run along the coast. They are best known in Kerala.

  • Their water is brackish (a mix of sea water and fresh water). It is used for fishing and for certain salt-tolerant paddy varieties and coconut. It is not used for drinking, so it adds little to the utilisable freshwater total.

Where it occurs

  • Water-rich basins: the Ganga, Brahmaputra and Barak basins cover about one-third of India's area but hold about 60% of its surface water.
  • Their rivers are perennial (they flow all year). They are fed by monsoon rain and Himalayan snow and glaciers.
  • The Brahmaputra and Barak basins in north-east India get very heavy monsoon rain.

  • The Ganga and Brahmaputra are still largely untapped.

  • Stressed peninsular basins: the Godavari, Krishna and Kaveri.

  • Their rivers depend on rain only, so they are seasonal.
  • Their catchments are smaller, and many lie in rain-shadow areas (the dry side of a mountain, away from the wind), such as east of the Western Ghats.

  • Most of their flow is already used, which leads to inter-state disputes such as the Kaveri dispute.

  • Lagoons and backwaters:

  • Vembanad (Kerala, Malabar coast): Kerala's largest lake, near Kochi and Alappuzha. It borders Kuttanad, where paddy is grown below sea level.
  • Ashtamudi (Kerala): near Kollam.
  • Chilika (Odisha, east coast): south-west of the Mahanadi delta. It is India's largest coastal lagoon.
  • Pulicat (Andhra Pradesh–Tamil Nadu border, Coromandel coast): north of Chennai.

  • Lagoons and lakes of West Bengal in the Ganga delta area.

  • Census of Water Bodies (2023, Ministry of Jal Shakti): the first national count. It found about 24.2 lakh water bodies. Most are rural ponds, and West Bengal has the largest number. Some are encroached (illegally occupied by buildings, farms or roads) or no longer in use.

Don't confuse with

  • Total water resource vs utilisable water resource: the total is what reaches rivers and aquifers (1,999.20 BCM). The utilisable part is what can actually be taken out (1,137 BCM) [2].
  • Precipitation vs total water resource: precipitation (~4,000 km³ NCERT; 3,880 BCM CWC) is the rain and snow that fall. The total water resource is what is left after evapotranspiration losses.
  • Replenishable groundwater vs deep (static) groundwater: replenishable groundwater is refilled by rain each year and is counted as usable (447 BCM) [2]. Deep groundwater is not refilled each year.
  • Brackish lagoon water vs freshwater: lagoons such as Chilika and Vembanad are partly salty. They support fishing and salt-tolerant crops but not drinking water.

Prelims Hooks

  • India: ~2.45% of world area, ~4% of world water, >17% of world population (NCERT; now ~18%).
  • CWC 2019: total water resource 1,999.20 BCM; utilisable 1,137 BCM = 690 surface + 447 groundwater (1985–2015) [2]. NCERT: 1,869 total; 1,122 utilisable = 690 + 432.
  • Trap: usable surface water is 690 in both the old and 2019 estimates. Only the groundwater figure changed [2].
  • About 10,360 rivers longer than 1.6 km. Only about 32% (690 cubic km) of their flow is usable (NCERT).
  • Ganga–Brahmaputra–Barak: ~one-third of area, ~60% of surface water. Already heavily used: Godavari, Krishna, Kaveri.
  • Lagoon–state pairs: Vembanad, Ashtamudi → Kerala; Chilika → Odisha; Pulicat → Andhra Pradesh–Tamil Nadu. First Census of Water Bodies (2023): ~24.2 lakh, with West Bengal having the most.

Mains Points

  • Paradox of plenty (GS-III): India has about 2,000 BCM of water a year, but only about 1,137 BCM can be used [2].
  • Rain is packed into the monsoon months, and relief limits where water can be stored.

  • So India is short of water in some places and seasons. More storage, groundwater recharge and rainwater harvesting are the answer.

  • Spatial imbalance (GS-I): about 60% of surface water is in the Ganga–Brahmaputra–Barak basins, while the peninsular basins are already over-used.

  • This explains floods in the north-east, and shortages and Kaveri-type disputes in the south.

  • It feeds the debate on inter-basin water transfer (river linking).

  • Reviving traditional and coastal water bodies (GS-III): the 2023 Census shows that most of India's 24.2 lakh water bodies are rural ponds, and that some are encroached or unused.

  • Community-led revival under drives such as the Jal Shakti Abhiyan is a low-cost way to recharge groundwater, with the Census as the baseline.
  • Lagoons such as Vembanad, Chilika and Pulicat face siltation, encroachment and salt-water intrusion, so they need wetland-based management.

Related concepts

Read more

Sources

  1. 1Class 12, Ch 4 "Water Resources" (primary)
  2. 2Central Water Commission, "Water Resource Estimation" (Reassessment of Water Availability, 2019)cwc.gov.in · tier 1