Singapore has an underground superhighway most people will never see.
It carries used water.
Instead of pumping sewage through many small treatment systems forever, the Deep Tunnel Sewerage System uses gravity to move used water through deep tunnels toward large central water-reclamation plants.
Did you know that the complete DTSS is designed as a 206 km network, costs around S$10 billion and is intended to serve Singapore for about 100 years?
This article targets Deep Tunnel Sewerage System Singapore, DTSS Singapore, Tuas Water Reclamation Plant, used water Singapore and sewer tunnel Singapore.
Official information was checked on 5 October 2026. Worked examples are fictional.
Did You Know? DTSS Is a 206 km Used-Water Superhighway
PUB describes the Deep Tunnel Sewerage System as a 206 km-long network of deep tunnels designed to convey used water by gravity to three centralised water-reclamation plants at Changi, Kranji and Tuas.
The system costs around S$10 billion and is designed for a 100-year lifespan.
Official reference: PUB — Deep Tunnel Sewerage System.
Gravity Replaces Many Pumping Stations
Traditional sewer systems often need pumping stations to lift used water over topographic constraints.
DTSS places major tunnels deep enough that gravity can carry used water toward central treatment plants.
Gravity has no motor to fail and no electricity bill.
The engineering investment upfront can reduce operating complexity over decades.
Worked Example: A Pumping Station Creates Lifetime Energy Cost
Imagine a fictional pumping station consumes 2 MW continuously.
Over one year that is about 17.5 GWh before downtime or load variation.
Over decades, electricity cost becomes enormous.
A gravity-based system can justify higher construction complexity if it removes enough lifetime pumping.
Phase 1 Was Completed in 2008
PUB’s DTSS Phase 1 includes a 48 km deep sewer tunnel, 60 km of link sewers and the Changi Water Reclamation Plant.
Official reference: PUB — DTSS Phase 1.
The first phase established the eastern backbone of the national used-water system.
Changi WRP Is a High-Capacity Treatment Hub
PUB states that Changi Water Reclamation Plant was initially designed for 800,000 m³ of used water per day and can ultimately be expanded to 2.4 million m³/day.
Centralising treatment allows large plants to use sophisticated process technology at scale.
Wastewater treatment becomes industrial infrastructure.
Phase 2 Extends the System Across Western Singapore
DTSS Phase 2 adds a 98 km network of deep tunnels and link sewers serving the western half of Singapore, including downtown and future developments such as Tengah and Jurong Lake District.
Official reference: PUB — DTSS Phase 2.
The second phase completes the national backbone.
Commissioning Is Now Scheduled in Phases From 2027
PUB’s current DTSS page says the complete Phase 2 network, including Tuas Water Reclamation Plant, is scheduled to be commissioned in phases from 2027.
Official reference: PUB — DTSS Current Project Status.
This supersedes older material that referenced earlier completion dates.
Phase 2 Tunnelling Was Completed in August 2023
The major tunnelling works were successfully completed in August 2023.
Current remaining works include corrosion-protection lining, link-sewer pipe jacking, site reinstatement and selected mechanical and electrical works.
The tunnel excavation milestone was not the same as completing the entire operating system.
Worked Example: Infrastructure Is a Chain of Commissioning
Imagine a tunnel is physically excavated but its gates, sensors, link sewers and downstream treatment plant are unfinished.
The tunnel exists and the service does not.
Large infrastructure becomes operational only when every critical link can function together.
Construction progress and service readiness are different metrics.
The Phase 2 Conveyance System Uses 49 km of Deep Tunnels and 49 km of Link Sewers
PUB’s dedicated Phase 2 conveyance page describes 49 km of deep tunnels and 49 km of link sewers carrying used water by gravity toward Tuas WRP.
Official reference: PUB — DTSS Phase 2 Conveyance System.
The network combines very deep main arteries with smaller connections feeding them.
Tunnel Isolation Gates Make Maintenance Possible
Phase 2 includes isolation gates that can divert flow to alternative routes so sections can be maintained.
Official reference: PUB — Tunnel Isolation Gates.
A century-long asset needs to be repairable without shutting down the whole city.
Maintainability is part of design.
Corrosion Protection Matters Underground
Used water creates corrosive conditions over long periods.
DTSS Phase 2 uses improved tunnel lining and a secondary corrosion-protection layer to increase resilience.
PUB also uses fibre-optic cables for real-time updates on tunnel structural integrity.
The sewer becomes a monitored civil structure.
Air-Flow Management Controls Odour and Gas
Large sewer tunnels move both water and air.
Pressure changes and gases can create odour and operational problems.
Phase 2 includes purpose-built air-flow-management systems to improve conditions along the network.
Underground hydraulics and ventilation are connected.
Tuas WRP Separates Domestic and Industrial Used Water
The future Tuas Water Reclamation Plant is designed with separate treatment streams for domestic and higher-strength industrial used water.
PUB’s current planning describes around 650,000 m³/day of domestic capacity and 150,000 m³/day of industrial capacity.
See Making Singapore Rich | Industrial Water Reuse, Wastewater Treatment and Resource Recovery.
DTSS Strengthens NEWater Supply
Used water conveyed through DTSS is treated at water-reclamation plants and can be further purified into NEWater.
The sewer therefore sits upstream of Singapore’s water-recycling strategy.
A wastewater tunnel becomes part of water security.
Worked Example: Collection Infrastructure Determines Recycling Capacity
A recycling plant capable of treating 1 million m³/day cannot use that capacity if the collection system delivers only 600,000 m³/day.
Treatment and conveyance have to scale together.
DTSS creates the transport backbone that allows centralised recycling plants to operate at scale.
DTSS Could Cut the Used-Water System’s Land Footprint by Half
PUB says that when DTSS is fully completed, older intermediate pumping stations and conventional water-reclamation plants can be phased out.
This is expected to reduce the used-water system’s overall land footprint by about half, freeing up to 150 hectares for higher-value use.
Official reference: PUB — DTSS Land Savings.
Infrastructure value appears both underground and in the land released above ground.
Worked Example: Underground Infrastructure Creates Surface Value
Imagine 150 hectares of obsolete utility land can eventually be repurposed.
That is 1.5 million square metres of land area before roads or redevelopment constraints.
The tunnel’s value therefore includes land-use flexibility as well as wastewater transport.
DTSS Connects to Tuas Nexus
Tuas WRP is co-located with NEA’s Integrated Waste Management Facility to form Tuas Nexus.
Water, sludge, food waste and energy streams can be integrated across the two facilities.
See Making Singapore Rich | Waste-to-Energy, Incineration and Landfill Engineering.
The sewer network eventually feeds a water-energy-waste platform.
DTSS Connects to Urban Planning
Tunnels preserve surface land for housing, parks, transport and business uses.
See Making Singapore Rich | Urban Planning, Master Plan 2025 and Land-Use Economics.
Deep infrastructure creates surface optionality.
The Risk: Deep Tunnelling Is Technically Difficult
Tunnels can run tens of metres below ground through varying geology and beneath developed areas.
Engineers need to manage ground movement, groundwater and existing infrastructure.
The invisible location does not make construction simple.
The Risk: One Long-Lived Tunnel Needs Repairability
A 100-year design life means components will need inspection and maintenance many times.
Isolation gates, monitoring and alternative flow paths reduce the risk that maintenance becomes a system shutdown.
Lifecycle design matters more than opening-day performance.
The Risk: Corrosion Happens Slowly
A tunnel can appear healthy for years while corrosive environments gradually attack concrete and reinforcement.
Protective lining and structural monitoring address a failure mode that develops over decades.
Long-lived infrastructure needs slow sensors for slow problems.
The Risk: Centralisation Concentrates Consequence
Centralised treatment creates scale and land efficiency.
It also means a major failure can affect a larger share of the system.
Redundancy, isolation and robust design become more important as centralisation increases.
DTSS Creates Specialist Engineering Capability
The programme requires tunnelling, geotechnical engineering, hydraulic design, corrosion science, structural monitoring and major project management.
Singapore can reuse that expertise in underground rail, utilities and overseas infrastructure.
One national project becomes a capability-building platform.
Education Builds Underground-Infrastructure Talent
Students can learn gravity flow, pipe capacity, geology, corrosion and lifecycle engineering through DTSS examples.
See Making Singapore Rich | Education, Skills and Human Capital.
A Guided Classroom Investigation
Give students two fictional sewer routes.
Route A uses five pumping stations.
Route B tunnels deeper and flows mostly by gravity.
Ask which costs more initially and which may cost less to operate for 100 years.
The exercise teaches lifecycle economics.
Independent Practice: Centralise or Distribute?
A fictional city can build ten small treatment plants or two large plants connected by deep tunnels.
Which is better?
Students should compare land, resilience, operating scale, pumping and maintenance.
The learning goal is infrastructure architecture.
What Progress Should Look Like
A stronger used-water economy should commission DTSS Phase 2 reliably, increase NEWater capacity, reduce pumping dependence, maintain long-lived tunnels and convert freed surface land into higher-value urban uses.
A stronger learner should distinguish tunnel completion from system commissioning, sewage disposal from water recycling and construction cost from century-long lifecycle value.
Frequently Asked Questions
How long is Singapore’s DTSS?
PUB describes the complete system as a 206 km network of deep tunnels.
How much does DTSS cost?
PUB says the two-phase system costs around S$10 billion.
How long is it designed to last?
About 100 years.
When will DTSS Phase 2 start operating?
PUB’s current project page says commissioning will occur in phases from 2027.
How much land can DTSS free?
PUB says the completed system can halve the overall land footprint of the used-water system and free up to about 150 hectares.
How does DTSS make Singapore richer?
It lowers long-run pumping needs, supports large-scale NEWater recycling, frees scarce land and builds world-class tunnelling and water-infrastructure expertise.
Helpful Reading and Singapore Graph Connections
- PUB — Deep Tunnel Sewerage System
- PUB — DTSS Phase 2 Conveyance System
- PUB — Tuas Water Reclamation Plant
- Making Singapore Rich | Industrial Water Reuse, Wastewater Treatment and Resource Recovery
Making Singapore Rich: Let Gravity Carry a Century of Used Water
Did you know that one of Singapore’s biggest water technologies is simply going downhill?
Deep tunnels remove pumping stations.
Central plants enable large-scale treatment.
NEWater turns used water into a new resource.
Surface land is released for other uses.
Singapore becomes richer when underground infrastructure solves several above-ground constraints at once.
The used water leaves the building.
DTSS turns that waste stream into the beginning of the next water cycle.