Groundwater in Nepal: Terai Aquifers, Tubewells & Kathmandu Valley

Although Nepal is famous for its Himalayan rivers, a large share of its people actually drink and irrigate with water pumped from beneath the ground. Just over half of Nepal's population lives in the Terai, the flat southern plain, according to the 2021 AD (2078 BS) census, and studies estimate that around 90 percent of Terai households depend on groundwater as their main source of drinking water, mostly through hand pumps and tubewells. Groundwater also supports dry-season irrigation of rice, wheat and vegetables where surface canals cannot reach.

Groundwater occurs very unevenly across the country. The thick, unconsolidated sediments of the Terai and of intermontane valleys such as Kathmandu and Pokhara hold the great majority of exploitable reserves, while in the hills and mountains groundwater emerges mainly as springs from fractured and weathered rock. This page consolidates the verified figures on the Terai reserve, tubewell systems, aquifer types, the Kathmandu Valley's over-extraction, and the Groundwater Resources Development Board (GWRDB).

The Terai plain is the northern edge of the Indo-Gangetic basin, filled with sand, gravel, silt and clay washed down from the Himalaya. Recent assessments, building on the academic overview 'Groundwater Resources of Nepal: An Overview' (Springer, 2018), put the annually renewable (dynamic) groundwater recharge of the Terai at roughly 8,800 million cubic metres (MCM) per year. Estimated extraction for domestic, irrigation and industrial use is about 1,935 MCM per year, meaning only around 22 percent of the annual recharge is currently used, so the region as a whole is under-exploited even though local stress points exist.

The main recharge belt is the Bhabar zone, a strip of coarse boulder and gravel deposits at the foot of the Siwalik (Chure) hills where rivers and monsoon rain sink rapidly underground. Water moving south from the Bhabar feeds both the shallow unconfined aquifers and the deeper confined aquifers of the plain; research in districts such as Nawalparasi also shows palaeochannels (buried old river courses) acting as recharge pathways. In coarse Terai sediments, permeability can reach 100 to 150 metres per day, which is why tubewells there yield water so readily.

GWRDB studies indicate that about 726,000 hectares of Terai land have good potential for shallow-aquifer (shallow tubewell) development and a further 305,000 hectares have marginal potential, while roughly 190,000 hectares could be irrigated by exploiting deep aquifers.

Nepali practice, following Asian Development Bank (ADB) and Department of Irrigation definitions, classifies a shallow tubewell (STW) as a well up to about 50 metres deep with a casing diameter under 10 centimetres; anything deeper or wider is a deep tubewell (DTW). In much of the Terai the upper unconfined aquifer, roughly the top 50 to 60 metres of sediment, is a highly productive shallow zone, and many hand-drilled or boring-set wells strike usable water within 10 to 30 metres. Hydrogeological studies in the western Terai commonly treat aquifers shallower than about 46 metres as 'shallow' and those below as 'deep' confined systems.

Deep tubewells penetrate confined aquifers below this shallow zone; most groundwater production in the Terai is limited to the upper 250 metres of sediment. DTWs are drilled by rigs, fitted with larger-diameter casing and submersible or turbine pumps, and can command tens of litres per second, enough for municipal supply or irrigating large blocks of land. Their high capital and energy cost has historically limited uptake, which is why donor projects, including recent efforts to solarise deep tubewells in the Terai, focus on reducing pumping costs.

Shallow tubewells drove Nepal's groundwater irrigation expansion because they suit smallholders: low investment, quick installation, and operation with small diesel, electric or increasingly solar pumps. GWRDB alone has constructed over 7,000 shallow tubewells irrigating around 22,000 hectares, and by the early 2000s an estimated 200,000 shallow tubewells had already been installed across 20 Terai districts by government, donor and private initiatives; private installation has continued to grow since.

Nepal's aquifers fall into three broad families. First are the unconsolidated alluvial sediments of the Terai and inner-Terai (dun) valleys such as Chitwan and Dang: alternating layers of gravel, sand and clay that form both unconfined shallow aquifers and confined deep aquifers, locally artesian where the confining clay pressure is high. These are by far the country's most important groundwater bodies.

Second are the fluvio-lacustrine fills of intermontane basins, above all the Kathmandu Valley and the Pokhara Valley, where old lake and river deposits several hundred metres thick store significant groundwater. Third are hard-rock aquifers of the hills and mountains: karstified and fractured carbonate rocks (limestone and dolomite) of the Midland zone and the Tethys sedimentary sequence can develop good localised aquifers, while elsewhere groundwater moves through fracture networks and weathered mantles that feed the springs on which most hill communities rely. The British Geological Survey and other surveys note that these mid-hill springs are typically perennial but shrink sharply in the winter and pre-monsoon months.

The Pokhara area is Nepal's best-known karst landscape: underground drainage in limestone has produced features such as Mahendra Cave, Gupteshwor Cave and the sinking flow at Patale Chhango (Davis Falls), where surface water disappears into karst conduits. Karst aquifers can transmit large volumes of water quickly, but they are also vulnerable to contamination because water receives little natural filtration in open conduits.

The Kathmandu Valley is a bowl-shaped intermontane basin filled with fluvio-lacustrine sediments of Plio-Pleistocene age, reaching about 500 to 600 metres thick in the centre; drilling records show the fill varying from 78 metres at Bansbari to 549 metres at Bhrikuti Mandap. Hydrogeologists divide the valley into three groundwater districts: a northern district of coarse sands and gravels (the main productive aquifer and recharge area, hosting well fields such as Bansbari, Dhobikhola, Gokarna and Manohara), a central district where a thick black lacustrine clay known locally as Kalimati confines the deep aquifer and limits recharge, and a smaller southern district of low-to-moderate productivity.

Extraction has grown far beyond natural replenishment. Pumping from deep wells rose from roughly 2.3 million litres per day (MLD) in 1979 to around 80 MLD by 2011, and recent reporting puts total deep-borewell extraction in the valley at over 100 MLD, of which the public utility Kathmandu Upatyaka Khanepani Limited (KUKL) accounts for the largest share, alongside thousands of private, hotel, industrial and tanker wells. A widely cited water-balance study estimated sustainable recharge at only about 9.6 million cubic metres per year against extraction of about 21.6 million cubic metres in 2001, meaning the valley was already pumping more than twice its recharge two decades ago.

The consequences are measurable: groundwater levels in parts of the valley fell by an estimated 13 to 33 metres between 1980 and 2000, and monitoring since then has recorded continuing declines, with recent reports citing average drops on the order of 0.8 metres per year and faster falls in heavily pumped zones. Traditional stone spouts (dhunge dhara) and shallow wells have dried across the urban core. The Melamchi Water Supply Project, whose first-phase 170 MLD supply reached Kathmandu in 2021 AD (2077/78 BS), is intended to reduce this dependence, though flood-related interruptions have kept the valley leaning on its wells. Extraction is licensed by the Kathmandu Valley Water Supply Management Board (KVWSMB), and municipal programmes now promote rainwater harvesting and recharge pits to replenish the aquifer.

The Government of Nepal established the Groundwater Resources Development Board (GWRDB, Bhumigat Jalsrot Bikas Samiti) in 1976 AD (2033 BS) under the then Ministry of Water Resources, as a development committee tasked with studying and developing the country's groundwater. Today it operates under the Ministry of Energy, Water Resources and Irrigation, with its head office at Babarmahal, Kathmandu, and branch (field) offices across the Terai at Biratnagar, Lahan, Mahottari, Birgunj, Chitwan, Butwal, Dang, Nepalgunj and Dhangadhi.

GWRDB's core work is investigation and monitoring rather than large-scale supply: it maps groundwater-potential areas through geophysical surveys, drills investigation tubewells into both shallow and deep aquifers, monitors water levels in observation wells, analyses water quality, and supports shallow and deep tubewell development for irrigation and drinking water. Its data underpin the national Groundwater Dashboard (gw-nepal.com), which publishes well records and monitoring information. The board has also drafted policy and legal instruments for groundwater management, an area where Nepal still lacks a dedicated act.

Quantity is not the only concern: quality problems shape how Nepal's groundwater can be used. The most serious is arsenic in shallow Terai aquifers, a natural contamination shared with the wider Ganges basin. In national blanket-testing campaigns summarised in the early-to-mid 2000s, about 23 percent of roughly 15,000 tested tubewells exceeded the World Health Organization guideline of 10 micrograms per litre and about 5 percent exceeded Nepal's interim national standard of 50 micrograms per litre, with Nawalparasi among the worst-affected districts. Deep aquifers are generally (though not always) safer, which is one reason deep tubewells are promoted for drinking supply in arsenic-prone areas. Shallow urban groundwater, including in the Kathmandu Valley, additionally suffers from ammonia, iron and microbial pollution from unsewered sanitation.

Governance remains the weak link. Nepal has no standalone groundwater act; abstraction is governed generally under the Water Resources Act, 2049 BS (1992), which vests water ownership in the state, plus valley-specific licensing by KVWSMB. Reviews carried out under the FAO-supported Groundwater Governance project and later academic analyses identify persistent gaps: no dedicated groundwater policy or institution with regulatory teeth, limited monitoring capacity across the three tiers of federal government, and weak data management. Because most of the Terai reserve is still unused while Kathmandu's is overdrawn, the policy challenge is double-sided, encouraging productive use of groundwater for irrigation in the plains while restraining and recharging extraction in the valley.