Overview
The Deep Tunnel Sewerage System (DTSS) is a massive underground superhighway for Singapore’s used water management, comprising 206 km of deep tunnel networks. The system connects to three centralised water reclamation plants (WRPs) at Changi, Kranji, and Tuas, representing a strategic national approach to water security for a population exceeding 6 million.
Singapore has four sources of potable water — referred to as the “Four National Taps” — to meet its needs. The DTSS underpins the third national tap: purified water reclaimed from used water at NEWater facilities, which now supplies approximately 55% of the nation’s water needs.
The DTSS is costing around $10 billion and is designed to last for 100 years. It is due to be fully operational in 2028.
Timeline & Location
The DTSS programme began with the commissioning of a feasibility study in 1997, receiving formal approval in 1998. The system is built at depths of 30–80 metres underground across Singapore, using tunnel boring machines (TBMs) to navigate the island’s complex geology.
Three water reclamation plants anchor the network: the Changi WRP, located on 32 hectares of reclaimed land with a capacity to treat 800,000 m³ of used water per day (expandable to 2,400,000 m³); the Kranji WRP; and the Tuas WRP, which integrates used water and solid waste treatment.
Stakeholders
Singapore utilities are not privatised; the system is owned and managed by the Government of Singapore through the Public Utilities Board (PUB), the national water agency.
Phase 2 of the DTSS is overseen by joint venture partners AECOM and Black & Veatch, appointed by PUB. Users and stakeholders of the system include government agencies, architects, construction firms, and engineers involved in Singapore’s national infrastructure planning.
The Four National Taps
Singapore’s water strategy is built around four diversified sources of potable water, known as the “Four National Taps”:
Digitalisation & Data
A digital twin (DT) was developed for the PUB Changi Water Reclamation Plant (Johnson et al. 2021). This DT encompasses the whole plant process — hydraulics and controls — and automatically accepts over 1,200 data streams from both SCADA and Laboratory Information Management systems.
Key data types supporting the DTSS include:
Geological Data
Extensive data from deep shaft excavations and TBM operations across Singapore’s geology (depths of 30–80 m) inform construction methods and structural integrity.
Engineering & Construction Data
Tunnel progress, materials used (e.g., specific concrete and HDPE lining for corrosion resistance), and equipment performance are meticulously tracked.
Operational Performance Data
Water flow velocity (mean velocity of 2.1 m/s in dry weather), water levels, air flow, and silt deposit accumulation help manage in-tunnel conditions and inform maintenance.
Monitoring & Sensor Data
DTSS Phase 2 incorporates fibre optic cables cast into tunnel linings for structural integrity monitoring and built-in sensors for remote monitoring. Real-time data collection is central to the “smart” WRP operations at Tuas.
Hydrological & Environmental Data
Scientific studies using hydrological models (1D-RFSM sewer-surface) determined optimal route and design capacity, exploring how the DTSS bolsters urban flood resilience.
References:
IWA Publishing — The transition of WRRF models to digital twin
SIWW 2022 — Bruce Johnson Presentation (PDF)
Hazards
Exogenous Hazards
Reductions in raw water (from rivers, lakes, and groundwater) cannot meet growing demand for potable water. Demand for land for development increases pressure on innovation for land used for water processing.
Endogenous Hazards
The increased risk of contamination of water supply due to pipe damage owing to infrastructure degradation over time.
Cost & Benefit
Cost: The DTSS is costing around $10 billion and is designed to last for 100 years.
Key Benefits: A significant reduction in land taken by used-water infrastructure — freed up for higher-value development — through the creation of three centralised collection and treatment points connected by the DTSS. The progressive phasing out of existing conventional WRPs and intermediate pumping stations frees up 150 hectares of land.
Resilience Principles Assessment
Assessment of meeting Principles of Resilient Infrastructure
Clearly Defined Accountabilities and Shared Responsibilities (P1)
Public utility leadership demonstrated by a portfolio approach to water security and long-term planning.
Proactively Protected (P2)
The DTSS is a massive underground superhighway comprising 206 km of deep tunnel networks. The Changi WRP, located on 32 hectares of reclaimed land, treats 800,000 m³ of used water per day with ability to expand to 2,400,000 m³.
Environmentally Integrated (P3)
At Tuas, the WRP and the Integrated Waste Management Facility (IWMF) will integrate used water and solid waste treatment processes to maximise synergies for both energy and resource recovery. The DTSS uses gravity to reduce the need for active energy pumping and the risk of pollution from rainwater catchments.
Socially Engaged (P4) To Do
National government engagement with society — details pending.
Adaptively Transforming (P5) To Do
Details pending.
Continually Learning and Improving (P6) To Do
Details pending.
Futures
Intentions for monitoring of water security using digital methods are under consideration. To Do