Melamchi Water Supply Project: Facts, Capacity & Timeline

The Melamchi Water Supply Project (MWSP), known in Nepali as Melamchi Khanepani Aayojana, is Nepal's largest drinking-water infrastructure undertaking. It transfers raw water from the Melamchi River — a tributary of the Indrawati River in Helambu, Sindhupalchok district — across a mountain divide into the Bagmati basin of Kathmandu Valley. The scheme was conceived to relieve the valley's chronic water shortage, where demand has long outstripped what local rivers, springs and depleting groundwater can supply.

The project is implemented by the Melamchi Water Supply Development Board (MWSDB), a dedicated government board formed in November 1998 (2055 BS) under what is now the Ministry of Water Supply. Within Kathmandu Valley, water-supply assets are owned and regulated by the Kathmandu Valley Water Supply Management Board (KVWSMB), while day-to-day treatment and distribution of Melamchi water is handled by Kathmandu Upatyaka Khanepani Limited (KUKL), the valley's water utility. KUKL's Project Implementation Directorate managed the valley-side works such as reservoirs and pipe networks.

In its first phase, the project diverts about 170 MLD (million litres per day) of fresh water into the valley. The long-term design envisages 510 MLD once water from the nearby Yangri and Larke rivers is added in a second phase, making Melamchi the backbone of Kathmandu's water security for decades to come.

The heart of the project is a gravity-flow headrace tunnel running from the intake at Ambathan in Helambu, Sindhupalchok, to the water treatment complex at Sundarijal on the north-eastern rim of Kathmandu Valley. The main tunnel is about 26 km long — official and media sources cite figures between 26 km and 26.5 km — and total tunnelling, including construction access adits, comes to roughly 27.5 km. It is widely described as the longest water-supply tunnel in South Asia.

The tunnel has a cross-sectional area of about 12.7 square metres and was deliberately sized for the project's ultimate flow of roughly 6 cubic metres per second, enough to carry the full 510 MLD planned after Phase II. Because the alignment falls continuously from the Melamchi intake to Sundarijal, water moves entirely by gravity, with no pumping required — a major advantage for operating costs in a country with frequent power constraints.

Tunnel excavation began in August 2009 and, after two changes of contractor, the final breakthrough was achieved in April 2018. Water released into the tunnel for testing on 22 February 2021 took several days to travel the full length, reaching Sundarijal on 6 March 2021 (Falgun 2077 BS).

Phase I of the Melamchi Water Supply Project is designed to deliver about 170 MLD of raw water — roughly 2 cubic metres per second — from the Melamchi River to Kathmandu Valley. At Sundarijal, the water is treated at a plant built with support from the Japan International Cooperation Agency (JICA); its Phase I capacity of 170 MLD was constructed in two modules of 85 MLD each, and the site is master-planned to expand to an ultimate 510 MLD.

From Sundarijal, treated water enters a bulk distribution system that carries it to nine service reservoirs positioned around the valley, from where KUKL distributes it through a rehabilitated network of about 670 km of pipelines. A related programme also envisaged upgrading around 540 km of sewerage and building or improving six wastewater treatment plants, recognising that more water flowing into homes also means more wastewater to manage.

To put 170 MLD in perspective, KUKL's annual report for fiscal year 2024/25 (2081/82 BS) put daily demand in the valley at about 514 MLD, while total production from all sources — including Melamchi — was around 322 MLD. Before Melamchi arrived, KUKL could typically supply only about 120 MLD in the dry season, so a functioning Melamchi roughly doubles the utility's dry-season output even though it does not close the gap entirely.

The second phase of the project is designed to add about 170 MLD each from the Yangri and Larke rivers, two Indrawati-basin rivers that lie upstream of and close to the Melamchi valley in Sindhupalchok. Together they would add 340 MLD, lifting the system's total capacity to 510 MLD — the figure the tunnel was sized for from the outset.

According to KUKL's Project Implementation Directorate, Phase II requires construction of roughly 11 km of additional tunnel connecting the Yangri and Larke intakes to the existing Melamchi tunnel, two new headworks, and an additional 340 MLD of treatment capacity within the Sundarijal water treatment plant premises. Because the trunk tunnel already exists, Phase II is substantially cheaper per litre than Phase I was.

Phase II remains at the study and preparation stage. Successive governments have instructed the Ministry of Water Supply to advance the Yangri and Larke works, and prime-ministerial directives to begin Phase II have been reported in state media, but as of 2026 no construction contract or firm completion date has been announced. Any figures for Phase II timing should therefore be treated as indicative.

The Asian Development Bank (ADB) has been the project's lead financier. ADB approved Loan 1820-NEP for the Melamchi Water Supply Project on 21 December 2000, and the loan became effective on 28 November 2001. At the time, the project was costed at about US$464 million, with a broad consortium behind it: ADB (US$120 million), the World Bank (US$80 million), the Japan Bank for International Cooperation (US$52 million), NORAD of Norway (US$28 million), Sida of Sweden (US$25 million), JICA (US$18 million), the OPEC Fund (US$14 million) and the Nordic Development Fund (US$9 million).

Several early partners later withdrew — most notably the World Bank in 2002 — and the project was restructured in 2008 with a revised cost of US$317.3 million. Under the restructured plan, financing came from ADB (US$137 million), JBIC (US$47.5 million), JICA (US$18 million), the Nordic Development Fund (US$10.5 million), the OPEC Fund (US$13.7 million) and the Government of Nepal (US$90.6 million). Overall, roughly 57 percent of project costs were loans, 16 percent grants and about a quarter direct government financing.

Costs continued to evolve as contractors changed: the Italian firm CMC di Ravenna's 2013 tunnel contract alone was worth about Rs 8.7 billion, and additional financing was mobilised after the 2021 flood for restoration works. JICA separately supported the Sundarijal water treatment plant, while ADB's companion Kathmandu Valley Water Supply Improvement Project financed distribution-network upgrades inside the valley.

Few Nepali infrastructure projects have a longer or more turbulent history than Melamchi. First studied in the late 1980s and formally launched with the creation of the Melamchi Water Supply Development Board in November 1998, the project passed through donor withdrawals, a Maoist-conflict-era slowdown, two contractor terminations, the 2015 earthquakes and a catastrophic flood before settling into its current seasonal operating pattern.

The milestones below are drawn from the Melamchi Water Supply Development Board, ADB project records and reporting by The Kathmandu Post and OnlineKhabar.

On 15 June 2021 (Asar 1, 2078 BS) — barely three months after the first water arrived in Kathmandu — an extreme flood and debris flow swept down the Melamchi valley from the high Himalayan headwaters. The disaster killed people across Helambu and Melamchi, including project workers, destroyed homes, bridges and access roads, and buried the project's headworks under an estimated 20 to 24 metres of boulders and sediment. A second flood on 1 August 2021 deposited further debris. Because the tunnel gates had been closed, the tunnel itself was spared serious damage.

Since December 2022 the project has operated on a seasonal cycle using a temporary diversion at the damaged headworks: water is sent to Kathmandu roughly from the post-monsoon months (around October or November) until the onset of the monsoon (around June), when diversion is halted to protect the tunnel from flood-borne debris. Supply resumed on this pattern in December 2022, January 2024 and October 2024, and most recently on 12 November 2025 after an 11-day interruption during a protest by flood-affected local residents, which ended with government commitments on compensation, local employment and road construction.

For a permanent fix, an ADB-supported study has recommended relocating the headworks about 500 to 600 metres upstream to a less hazard-exposed site, which would require extending the tunnel by roughly 900 metres. The final design and construction timetable were still awaiting government decision as of 2024-2026, so year-round Melamchi supply remains a future goal rather than a current reality.

Kathmandu Valley's population of around three million faces one of South Asia's most acute urban water shortages. With demand estimated at about 514 MLD in fiscal year 2024/25 and total utility production of only around 322 MLD even with Melamchi flowing, households have long depended on rationed piped supply, private tankers, wells and jar water. Decades of groundwater over-extraction have also caused water tables in the valley to fall steadily.

When Melamchi water is flowing, its 170 MLD accounts for roughly half of KUKL's total production and transforms dry-season supply, allowing the utility to expand its distribution schedules across the valley's service reservoirs. When the monsoon shutdown comes, the valley falls back on older, smaller sources, and shortages return — which is why the timing of each year's resumption is front-page news in Nepal.

In the longer term, completing the permanent headworks and the Yangri-Larke second phase would take the system to 510 MLD, close to the valley's present demand. Until then, the Melamchi Water Supply Project remains both Kathmandu's greatest hydraulic achievement and an unfinished promise: a 26 km tunnel that works, waiting for headworks that can survive its Himalayan river.