Deep Tunnel Sewerage System

Singapore Infopedia


The Deep Tunnel Sewerage System (DTSS) was conceptualised in the 1990s as a sustainable, cost-effective solution to meet Singapore’s used water collection, treatment, reclamation and disposal needs in the long run. Spanning two phases over more than 20 years, Phase 1 was completed in 2008 while Phase 2 is due to be completed by 2025.

In the late 1960s, the Public Works Department drew up the Sewerage Master Plan to guide the development of a comprehensive sewerage system to cope with rapid population growth and industrialisation in post-independence Singapore, as well as to improve the quality of life. The master plan divided Singapore into six sewage catchment zones, each served by a sewage treatment works (later renamed water reclamation plants). Pumping stations channelled sewage to these plants, where it was treated to international standards before being discharged into the sea. The implementation of the master plan meant that all of Singapore was served by a modern sanitation system by 1997.1

However, Singapore’s water supply faced an increased risk of contamination due to pipe damage owing to infrastructure degradation over time. Another issue with the existing system was the large land area occupied by treatment plants and pumping stations. To address these problems, the government sought a sustainable long-term alternative that would allow Singapore to meet its growing needs without a need for continual expansion and upgrading. This led to the conception of the Deep Tunnel Sewerage System (DTSS) in 1995.2

In March 1997, then Minister for the Environment Yeo Cheow Tong revealed that the government had commissioned a feasibility study for DTSS.3 Then Prime Minister Goh Chok Tong confirmed the following year that the project would be implemented.4

The DTSS project comprises four components: two deep tunnel sewers; two water reclamation plants (WRPs); a network of link sewers; and deep-sea outfall pipes. Both deep tunnels have diameters of up to 6 m and stretch across Singapore at depths of up to 55 m underground. They are connected to the existing sewerage system by the smaller link sewers that divert used water flows from the existing sewers into the deep tunnels. Used water is conveyed through the deep tunnels entirely by gravity to three WRPs located in Kranji, Changi and Tuas at the northern, eastern and western ends of Singapore respectively. The Kranji WRP was an existing facility, while the Changi and Tuas WRPs are new ones built under the DTSS project. After being treated at the WRPs, the reclaimed water is channelled to NEWater factories and further purified into NEWater. Any excess treated water is discharged into the sea through the outfall pipes.5

Phase 1
Work on Phase 1 of the DTSS project commenced in 2000 and was completed in 2008 at a cost of S$3.4 billion.6

This phase comprised a new WRP at Changi, two 5 km-long deep-sea outfall pipes, 60 km of link sewers, as well as 48 km of deep tunnel sewers made up of two sections, namely, the North Tunnel running between the Kranji and Changi WRPs, and the Spur Tunnel extending westward from the North Tunnel. The Changi WRP has the capacity to treat 900,000 cu m of used water per day. In 2010, a NEWater factory was built atop the WRP. Treated used water from the WRP is directed to the NEWater factory and further purified for reuse, with any excess discharged into the sea.7

Phase 2
Construction for Phase 2 began in 2017 and is scheduled to be completed by 2025.8 Estimated to cost S$6.5 billion, Phase 2 encompasses a new WRP at Tuas along with its corresponding outfall pipe, 40 km of deep tunnel sewers and 60 km of link sewers.9

While Phase 1 serves the eastern part of Singapore, Phase 2 covers the western and southern parts of the island. In this phase, domestic used water and industrial used water will be conveyed separately through the South Tunnel and Industrial Tunnel respectively. The South Tunnel will be connected via a short Spur Tunnel to the existing deep tunnels built in Phase 1.10 The South and Industrial tunnels both lead to the Tuas WRP, which will have the capacity to treat 800,000 cu m of used water per day. A NEWater factory integrated with the WRP will facilitate the recycling of used water into NEWater.11

The Tuas WRP will also be co-located with the National Environment Agency’s Integrated Waste Management Facility (IWMF). Collectively called Tuas Nexus, both facilities will allow Singapore to harness potential synergies in the water-energy-waste nexus. For example, food waste from the IWMF will be co-digested with sewage sludge at the WRP to produce a higher yield of biogas (a form of biofuel produced through the decomposition of organic matter). The biogas is then conveyed to the IWMF to improve the thermal efficiency of the incineration plant, thereby boosting electricity production. The electricity generated at the IWMF will fully power both facilities at Tuas Nexus, with excess electricity fed to the grid.12

Singapore’s sewerage system previously consisted of six water reclamation plants, one sludge treatment works and 139 pumping stations located islandwide.13

After the completion of DTSS Phase 1 in 2008, the Kim Chuan, Seletar and Bedok WRPs, as well as the Serangoon Sludge Treatment Works, were closed progressively.14 Once Phase 2 commences operations, the Ulu Pandan and Jurong WRPs will also be phased out.15 The numerous pumping stations used in the conventional conveyance system will be phased out too, since gravity is used in DTSS to transport used water to the WRPs.16

The implementation of DTSS will eventually halve the land area occupied by used water infrastructure, which was 300 ha in the 1990s. The completion of Phase 1 has already reduced this to 190 ha. By freeing up land for other developments, DTSS has allowed Singapore to optimise the use of this scarce resource.17 For instance, the land once used by the Seletar WRP is now occupied by Seletar Aerospace Park.18

Two other advantages of DTSS are: It does not need to be continuously upgraded and expanded;19 and it has eliminated the risk of used water contaminating water catchments due to failures at the pumping stations or breakages in the mains since intermediate pumping systems are no longer needed.20

Recognised as an outstanding engineering innovation, the DTSS project received the Institution of Engineers Singapore Prestigious Engineering Achievement Award and the ASEAN Outstanding Engineering Achievement Award in 2005, as well as the International Water Association’s Project Innovation Award in 2008.21

Centre for Liveable Cities

1. Tan Yong Soon, Lee Tung Jean and Karen Tan, Clean, Green and Blue: Singapore’s Journey Towards Environmental and Water Sustainability (Singapore: ISEAS Publishing, 2009), 182–83 (Call no. RSING 363.70095957 TAN); Tan Gee Paw, Water (Singapore: Institute of Policy Studies; Straits Times Press Pte Ltd, 2016), 29. (Call no. RSING 363.61095957 TAN)
2. Tan, Lee and Tan, Clean, Green and Blue, 187–88; Tan, Water, 29–30.
3. Yeo Cheow Tong, “The Ground-Breaking Ceremony of the Ulu Pandan Sewerage Treatment Works Compact and Convered Extension,” speech, 25 March 1997, transcript, Ministry of Information, Communications and the Arts. (From National Archives of Singapore document no. 1997032501)
4. Goh Chok Tong, “National Day Rally Speech in English,” speech, Kallang Theatre, 23 August 1998, transcript, Ministry of Information, Communications and the Arts. (From National Archives of Singapore document no. 1998082302)
5. Ministry of the Environment and Water Resources, “Deep Tunnel Sewerage System (DTSS),” press release, 20 January 2001 (From National Archives of Singapore document no. MEWR20010120001); PUB, “Factsheet: About the Deep Tunnel Sewerage System (DTSS),” 20 November 2017 (From National Archives of Singapore); “About Deep Tunnel Sewerage System,” PUB, accessed 26 October 2019.
6. Lee Yock Suan, “The Ground-Breaking Ceremony for the Deep Tunnel Sewerage System Contract T-05 Kranji Tunnel,” speech, Mandai Road, 8 July 2000, transcript, Ministry of The Environment (For National Archives of Singapore document no. MSE_20000708001); “Phase 1,” PUB, accessed 23 October 2019.
7. PUB, “About Deep Tunnel Sewerage System”; PUB, “Factsheet: About the Deep Tunnel Sewerage System (DTSS),” 20 November 2017 (From National Archives of Singapore); PUB, “Phase 1.”
8. Navin Sregantan, “PUB Starts Second Phase of DTSS with S$2.3B of Work Contracted Out,” Business Times, 20 November 2017.
9. Woo Lai Lynn and Ganeshan Vallipuram, Deep Tunnel Sewerage System (DTSS) Phase 2 (Singapore: PUB, 18 February 2016)
10. PUB, Singapore's National Water Agency, “PUB Breaks Ground for Conveyance System of Deep Tunnel Sewerage System Phase 2,” press release, 20 November 2017 (From National Archives of Singapore document no. 20171120003); PUB, “Deep Tunnel Sewerage System (DTSS).”
11. “Sewage Superhighway,” Straits Times, 21 November 2017 (From Factiva via NLB’s eResources website); “Tuas WRP DTSS 2 Industry Briefing,” PUB, Singapore's National Water Agency,” accessed 23 October 2019.
12. National Environment Agency, Singapore, “PUB and NEA to Call Over S$5 Billion in Tenders for Tuas Nexus,” press release, 9 July 2018.
13. PUB, “Deep Tunnel Sewerage System (DTSS).”
14. Yue Choong Kog, “Transboundary Urban Water: The Case Study of Singapore and Malaysia,” in Understanding and Managing Urban Water in Transition, et al. ed., Quentin Grafton (Springer: Dordrecht, 2015), 586.
15. PUB, “Deep Tunnel Sewerage System (DTSS).”
16. Tan, Lee and Tan, Clean, Green and Blue, 189.
17. “Benefits,” PUB, accessed 23 October 2019.
18. Siau Ming En, “Construction Begins for S$6.5 Billion, 100km Superhighway for Used Water,” Today, 20 November 2017.
19. Tan, Lee and Tan, Clean, Green and Blue, 189.
20. Tan, Lee and Tan, Clean, Green and Blue, 189; Tan, Water, 29–31.
21. Tan, Lee and Tan, Clean, Green and Blue, 188.

Further resources
Centre for Liveable Cities, Singapore and Public Utilities Board, Singapore, Water: From Scarce Resource to National Asset (Singapore: Cengage Learning Asia, 2012). (Call no. RSING 333.91095957 WAT)

D. A. Paulo and A. D’Souza, “The Long Road to Ensuring That Singapore’s Waste Doesn’t Go to Waste,” Channel NewsAsia, 17 February 2018. (From Factiva via NLB’s eResources website)

PUB, “Tuas Nexus,” press release, accessed 23 October 2019.

The information in this article is valid as at November 2019 and correct as far as we are able to ascertain from our sources. It is not intended to be an exhaustive or complete history of the subject. Please contact the Library for further reading materials on the topic.





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