SINGAPORE – The second phase of an underground “superhighway” to transport used water across the island started construction work on Monday (Nov 20).

When completed in 2025, Deep Tunnel Sewerage System (DTSS) Phase 2 will channel used water in the western parts of the island by gravity to a new water reclamation plant in Tuas.

The $6.5 billion project by water agency PUB will also free up 83ha of land – about the size of 116 football fields – currently housing the Ulu Pandan and Jurong Water Reclamation Plants, about 70 pumping stations and many more sewage treatment plants.

Minister for the Environment and Water Resources Masagos Zulkifli marked the start of construction at a ground-breaking ceremony held in Penjuru Road in Jurong East.

He said: “We have experienced how unpredictable weather patterns can be, and we expect dry seasons to worsen with climate change. It is therefore critical to augment our water sources by reclaiming water, so it can be used again and again, in an endless cycle.”

DTSS Phase 2 will give a boost to our Newater supply, he added.

One of the world’s largest projects of its kind, DTSS will eventually channel all of the island’s used water by gravity to water reclamation plants in Changi, Kranji and Tuas, where it is treated and then purified to produce Newater, or discharged into the sea.


The tunnels, which sit under the Republic’s railway network and above its electricity grid, slope downwards towards the three plants as they are dug at a gradient.

Phase 1, which cost $3.4 billion, was completed in 2008. It serves the eastern parts of Singapore, channelling used water to the Kranji and Changi Water Reclamation Plants.

DTSS Phase 2 will stretch 30km across the western part of Singapore, starting under Keppel Road, at 35m below ground, following the Ayer Rajah Expressway (AYE) all the way to Tuas Bay, where it will be 55m below ground. It will also include a separate 10km tunnel in Tuas for industrial used water.


PUB has appointed five contractors to design and build the tunnels, including home-grown company Koh Brothers Eco Engineering.

The system will also comprise 60km of link sewers, which will convey used water from existing sewerage network to the DTSS.

The 30cm thick tunnels in DTSS Phase 2 will be constructed with several safety features.

Guests looking at an informational map of the Deep Tunnel Sewerage System Phase 2 during the groundbreaking ceremony. ST PHOTO: MARK CHEONG

They will be lined with a special concrete and high density polyethylene (a type of plastic), which protect against corrosion, particularly from bacteria and other microorganisms, and the gaseous fumes from sewage. Sections under the sea will have an additional waterproof membrane layer.

Fibre optic cables will be embedded in the concrete lining, which will be used to monitor the structural integrity of the tunnels remotely, and detects things such as cracks.

There will be 18 shafts, which will allow human access. Each will come with gates that can be lowered to isolate certain sections of the tunnels for repair works.

Air jumpers, essentially giant fans, within the tunnels will be used to direct sewage fumes to four odour control facilities.

With these features, the tunnels are expected to last 100 years.

Mr Yong Wei Hin, director of DTSS Phase 2 at PUB, said the construction “will pose a new set of exciting challenges for us”.

 “There are a lot of sedimentary rocks and cavities along the way, which is not ideal for tunneling,” he added.

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