1
Delaware Aqueduct
New York City's main water-supply tunnel, completed in 1945, runs for 137 km at a diameter of 4.1 m. It is the longest continuous tunnel of any kind in use.
Location: New York State, USType: Water supplyCompleted: 1945
Top 10 Longest Water Supply Tunnels in the World
The ten longest water-supply tunnels in use, which are also the longest tunnels of any kind: from New York's 137 km Delaware Aqueduct to Shanxi's 43.5 km Yellow River diversion tunnels.
Quick answer
The Delaware Aqueduct, New York City's main water-supply tunnel, is the longest tunnel in use at 137 km. Finland's Päijänne Water Tunnel (120 km) is second and China's Dahuofang Water Tunnel (85.32 km) third. Rankings use continuous tunnel length from Wikipedia's List of longest tunnels as of October 2026.
The world's longest tunnels do not carry trains or cars; they carry water. The two longest tunnels in use anywhere, New York's Delaware Aqueduct and Finland's Päijänne tunnel, both bring drinking water to major cities, and both are more than twice as long as the longest railway tunnel, the 57.1 km Gotthard Base Tunnel. This list ranks water-supply tunnels only, so that every entry is measured on the same basis. Railway, metro, road, hydroelectric and wastewater tunnels are excluded; the site's railway-tunnel list covers rail.
Length (km)
137
Delaware Aqueduct 120
Päijänne Water Tunnel 85.3
Dahuofang Water Tunnel 82.8
Orange-Fish River Tunnel 82
Bolmen Water Tunnel 52.0
Želivka Water Tunnel 48.4
Arpa-Sevan Tunnel 44.6
Pahang-Selangor Raw Water Transfer Tunnel 43.7
Yellow River Diversion to Shanxi, North Line Tunnel No. 1 43.5
Yellow River Diversion to Shanxi, South Line Tunnel No. 7 The ranking
2
Päijänne Water Tunnel
Bored through solid rock, the 120 km Päijänne tunnel carries raw water from Lake Päijänne to the Helsinki metropolitan area. It opened in 1982 and is the second-longest tunnel in use.
Location: Southern FinlandType: Water supplyCompleted: 1982
3
Dahuofang Water Tunnel
Completed in 2009, the 85.32 km Dahuofang tunnel in Liaoning province has an 8 m diameter bore, and is the longest water-supply tunnel in Asia in the source table.
Location: Liaoning, ChinaType: Water supplyCompleted: 2009
4
Orange-Fish River Tunnel
The 82.8 km Orange-Fish River Tunnel diverts water from the Orange River to the Great Fish River in South Africa's Eastern Cape. The list of longest tunnels describes it as the longest continuous enclosed aqueduct in the Southern Hemisphere.
Location: South AfricaType: Water supplyCompleted: 1972
5
Bolmen Water Tunnel
Completed in 1987, the 82 km Bolmen tunnel runs between Kronoberg and Scania in southern Sweden, with a cross-section of about 8 square metres.
Location: Kronoberg and Scania, SwedenType: Water supplyCompleted: 1987
6
Želivka Water Tunnel
The 51.97 km Želivka tunnel, finished in 1972, brings drinking water from the Želivka reservoir to Prague.
Location: Central Bohemian Region, Czech RepublicType: Water supplyCompleted: 1972
7
Arpa-Sevan Tunnel
Built in the Soviet era and completed in 1981, the 48.36 km Arpa-Sevan tunnel transfers water from the Arpa river into Lake Sevan to help restore the lake's level.
Location: ArmeniaType: Water supplyCompleted: 1981
8
Pahang-Selangor Raw Water Transfer Tunnel
The 44.6 km tunnel of the Pahang-Selangor Raw Water Transfer Project, completed in 2014, carries raw water from Pahang to Selangor. Its bore is 5.2 m in diameter.
Location: Pahang and Selangor, MalaysiaType: Water supplyCompleted: 2014
9
Yellow River Diversion to Shanxi, North Line Tunnel No. 1
Tunnel No. 1 of the North Line of the Yellow River diversion project in Shanxi province is 43.67 km long and was completed in 2011.
Location: Shanxi, ChinaType: Water supplyCompleted: 2011
10
Yellow River Diversion to Shanxi, South Line Tunnel No. 7
Tunnel No. 7 of the South Line of the same Shanxi diversion project is 43.5 km long and was completed in 2002, just 170 m shorter than North Line Tunnel No. 1.
Location: Shanxi, ChinaType: Water supplyCompleted: 2002
Full comparison
| # | Name | Location | Type | Completed |
|---|---|---|---|---|
| 1 | Delaware Aqueduct | New York State, US | Water supply | 1945 |
| 2 | Päijänne Water Tunnel | Southern Finland | Water supply | 1982 |
| 3 | Dahuofang Water Tunnel | Liaoning, China | Water supply | 2009 |
| 4 | Orange-Fish River Tunnel | South Africa | Water supply | 1972 |
| 5 | Bolmen Water Tunnel | Kronoberg and Scania, Sweden | Water supply | 1987 |
| 6 | Želivka Water Tunnel | Central Bohemian Region, Czech Republic | Water supply | 1972 |
| 7 | Arpa-Sevan Tunnel | Armenia | Water supply | 1981 |
| 8 | Pahang-Selangor Raw Water Transfer Tunnel | Pahang and Selangor, Malaysia | Water supply | 2014 |
| 9 | Yellow River Diversion to Shanxi, North Line Tunnel No. 1 | Shanxi, China | Water supply | 2011 |
| 10 | Yellow River Diversion to Shanxi, South Line Tunnel No. 7 | Shanxi, China | Water supply | 2002 |
How we ranked this
Tunnels are ranked by continuous length in kilometres. Inclusion is limited to tunnels in use that Wikipedia's List of longest tunnels (permanent revision 1380706012, 17 October 2026) classifies as 'Water supply'. That list covers continuous tunnels of at least 13 km and excludes buried pipelines. Railway, metro, road, hydroelectric and wastewater tunnels are excluded, as are tunnels under construction. Lengths, locations and completion years are taken from that single table; lengths are shown as the table gives them. Rank 1 is the longest.
FAQ
What is the longest tunnel in the world?
The Delaware Aqueduct in New York State, a water-supply tunnel completed in 1945, is the longest tunnel in use at 137 km. Finland's Päijänne Water Tunnel (120 km) is second.
What is the longest railway tunnel?
The Gotthard Base Tunnel in Switzerland, at 57.1 km, opened in 2016. It is followed by Japan's Seikan Tunnel (53.85 km) and the Channel Tunnel (50.45 km).
What is the longest road tunnel?
Norway's Lærdal Tunnel, at 24.51 km, opened in 2000, is the world's longest road tunnel.
Why are metro lines not included?
Wikipedia's list also counts some fully underground metro lines as continuous tunnels; the longest, Suzhou Metro Lines 3 and 11, is listed at 86.5 km. Metro, rail, road, hydroelectric and wastewater tunnels are measured differently and are left out so that this list compares one type of tunnel.
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