Groundwater depletion

Also called: Groundwater overexploitation, Groundwater over-exploitation · Topic: Water Resources of India: Availability, Use and Conservation · NCERT: Class 6, Ch 3 "Landforms and Life"; Class 7, Ch 1 "The Story of Indian Farming"; Class 8, Ch 1 "Natural Resources and Their Use"; Class 10, Ch 3 "Water Resources"; Class 12, Ch 4 "Water Resources"

Meaning

Groundwater depletion (also called groundwater over-exploitation) happens when more water is pumped out of an aquifer each year than rain, canals and rivers put back. As a result, the water table (the top level of underground water) keeps falling. It matters because wells dry up and pumping costs rise. It also threatens India's long-term food security, and heavy pumping can bring harmful substances like arsenic, fluoride and uranium into drinking water.

Explanation

Basic terms

• Groundwater: water stored underground in the gaps between soil, sand and rock.
• Aquifer: a layer of rock or sediment that holds this water and lets it flow. Wells and tubewells draw water from aquifers.
• Water table: the top level of this underground water.
• Recharge: rain, canal water and river water soaking down into the aquifer and refilling it.
• Stage of groundwater extraction: the water taken out in a year, shown as a percentage of the water that can safely be taken out in a year.
• Above 100% → the aquifer is being "mined". More water leaves it each year than enters it.

How depletion works (cause → process → result)

• Extraction is greater than recharge
• The aquifer slowly empties.

• The water table falls.

• Pumps must lift water from deeper down

• They use more electricity or diesel.

• Pumping costs rise.

• Shallow wells and hand pumps go dry

• Wells fail.

• Farmers drill deeper and pay even more.

• Depletion makes water quality worse

• Over-withdrawal raised fluoride in Rajasthan and Maharashtra and arsenic in parts of West Bengal and Bihar.
• Older, deeper water often holds more dissolved fluoride.

• Heavy pumping pulls water quickly through arsenic-rich sediments, so more arsenic ends up in the water.

• Coastal aquifers turn salty

• Too much pumping near the coast lowers the pressure of fresh groundwater.
• Seawater moves inland into the aquifer. This is called salinity intrusion.

Causes of depletion in India

• Green Revolution tubewells:
• From the 1960s, HYV (high-yielding variety) seeds of wheat and paddy spread.
• Paddy needs standing water for months. It is not a natural crop for semi-arid Punjab.

• Demand for irrigation water rose sharply in Punjab, Haryana and western Uttar Pradesh.

• Free farm electricity:

• Running pumps longer cost farmers nothing extra.

• This led to over-pumping.

• Private pumping in villages and cities:

• Farmers run their own private tubewells. Urban housing societies pump from their own borewells.

• Together they empty aquifers faster than rain can refill them.

• Less river water reaching aquifers:

• The Ganga basin, which feeds over 500 million people, is under stress from changing glacier melt, water diverted away from the river, heavy pumping and dams.

• Less water stays in the river, so less soaks down into the aquifers below.

• Side-effect: soil salinity (salt building up in soil)

• Too much water and poor drainage make the water table rise in some places, or water evaporates from the surface.
• The salts are left behind as a white crust, and crop yields fall.

How CGWB classifies areas

• The CGWB (Central Ground Water Board) and the states assess groundwater in assessment units (blocks, mandals or talukas).
• 2024 assessment [2][3]:

Category	Units (2024)	Share
Safe	4,951	73.4%
Semi-critical	711	10.5%
Critical	206	3.05%
Over-exploited	751	11.1%
Total	6,746	—

• National stage of extraction: 60.47% (2024) [2].
• The trend is improving: over-exploited units fell from 17.24% (2017) to 11.13% (2024) [2][3].
• Yearly recharge rose by about 15 BCM (billion cubic metres) [2].
• Extraction fell by about 3 BCM over the same period [2].

Where it occurs

• North-west India is the core of over-exploitation: parts of Punjab, Haryana, Delhi and western Uttar Pradesh [4].
• States above 100% extraction: Punjab, Haryana and Rajasthan. Each of the three had more over-exploited units in 2022 than in 2017 [4].
• Punjab, the worst case:
• Stage of extraction was 165.99% in the 2022 assessment [4]. The 2024 assessment put it at about 156%, with about three-quarters of its blocks over-exploited.
• NCERT classes about 80% of Punjab's area as overexploited. Across a large part of the state, water lies deeper than about 30 m (NCERT Fig. 1.17, June 2022 map).

• Malwa (the part of Punjab south of the Sutlej) has uranium in 9 districts: Bathinda, Moga, Faridkot, Fatehgarh Sahib, Ferozepur, Ludhiana, Muktsar, Patiala and Sangrur [5]. Arsenic above the safe limit has been found in Mansa, Faridkot and Sangrur [5].

• Rajasthan: 151.07% stage of extraction (2022) [4]. Pumping has also raised fluoride levels.

• Fluoride belt linked to over-withdrawal: Rajasthan, Maharashtra, Telangana (Nalgonda district), Andhra Pradesh, Gujarat and Karnataka. These are the dry hard-rock areas of the Peninsula and the edge of the Thar.
• Arsenic belt: the Ganga-Brahmaputra plains of West Bengal, Bihar, Uttar Pradesh and Assam, continuing into Bangladesh. It is the world's worst-known arsenic belt.
• Coastal salinity intrusion: Saurashtra (Gujarat) and coastal Tamil Nadu.
• Ganga basin: stressed by groundwater pumping, dams, water diversion and changing glacier melt. It feeds over 500 million people.

Don't confuse with

• Groundwater contamination: depletion is about the amount of water (the water table falls). Contamination is about quality: harmful substances go above BIS (Bureau of Indian Standards) drinking-water limits. Depletion can make contamination worse, but the two are different problems.
• Geogenic vs anthropogenic contamination: arsenic, fluoride and uranium come naturally from rocks and sediments (geogenic). Nitrate comes from human activity such as fertiliser and sewage (anthropogenic). Arsenic in India is not mainly industrial.
• Waterlogging and soil salinity: these come from too much surface irrigation and poor drainage, which can make the water table rise in places. Depletion means the water table falls. Both can happen in the same intensively irrigated belt.
• "Over-exploited" vs "critical" units: over-exploited units take out more than 100% of the water that can safely be taken out each year. Critical units are the category just below that. In 2024 there were 751 over-exploited units and 206 critical units [2][3].

Prelims Hooks

• CGWB 2024: 751 of 6,746 assessment units (11.1%) are over-exploited. The national stage of extraction is 60.47% [2][3].
• Trap: India's groundwater did not simply get worse. Over-exploited units fell from 17.24% (2017) to 11.13% (2024) [2].
• States with a stage of extraction above 100%: Punjab, Haryana, Rajasthan. Punjab was at 165.99% and Rajasthan at 151.07% in 2022 [4].
• Over-withdrawal raised fluoride → Rajasthan and Maharashtra and arsenic → West Bengal and Bihar. Seawater intrusion from coastal pumping affects Saurashtra and coastal Tamil Nadu.
• Uranium in groundwater belongs to the Malwa belt of Punjab (Bathinda, Moga, Faridkot and others) [5].
• The Punjab Preservation of Subsoil Water Act, 2009 bans paddy transplanting before a notified date in June, which saves groundwater in the hottest weeks.

Mains Points

• Causes (GS-III): The HYV wheat–paddy cycle since the 1960s, free farm power, uncontrolled tubewells and urban borewells are the main causes. Aquifers are emptied faster than rain can refill them. North-west India (Punjab, Haryana, Delhi, western UP) is the over-exploited core, with Punjab at 165.99% (2022) [4]. Punjab became India's "granary" in the short term at a long-term cost to its water.
• Effects: The water table falls, pumping costs rise, wells fail, soil becomes saltier and long-term food security is at risk. Pumping also brings arsenic (Ganga-Brahmaputra plains), fluoride (Rajasthan, Maharashtra, Nalgonda) and uranium (Malwa) into drinking water. Coastal pumping draws seawater into aquifers in Saurashtra and Tamil Nadu. Depletion is therefore a farm crisis and a public-health crisis at the same time.
• Policy responses:
• CGWB assessments track how much groundwater each area has and uses.
• Punjab's 2009 subsoil water law delays paddy planting.
• DSR (direct-seeded rice) sows seed straight into the field and uses less water.
• Crop diversification moves farms to maize, pulses, cotton or fruit.
• Power-subsidy reform means metering farm power or paying farmers who use less.
• Better use of canal water and rainwater recharge reduce pumping and dilute fluoride.
• The fall from 17.24% to 11.13% over-exploited units between 2017 and 2024 shows that recharge works [2].

Related concepts

• Punjab groundwater crisis
• Arsenic contamination
• Fluoride contamination
• Groundwater contamination belts

Read more

• Groundwater depletion and contamination