Over a billion people worldwide face water scarcity and over two billion face issues with water sanitation, according to some estimates. This is a problem exacerbated by climate change, pollution, inefficient irrigation, and competition between population and industrial needs.

This includes the developed nation of Singapore, which has had a long history of water shortages and has even implemented water rationing at times. However, they have a master plan to help establish water sufficiency, which relies on four resources of water supply. These include:

Harvesting the wastewater is a critical aspect of this plan, which required Singapore to make a hefty investment.

A sewer superhighway

Singapore has invested in the Deep Tunnel Sewerage System (DTSS), which is a superhighway of underground tunnels that helps the nation fulfill its water reclamation services. Roughly 206 km of tunnels, up to 55 m below ground, transfer wastewater to three water reclamation plants (WRP): Changi, Kranji and Tuas.

Source: Singapore National Water AgencySource: Singapore National Water Agency

The entire DTSS required two phases of construction and S$10 billion. It was conceptualized back in the 1990s. The first phase was completed in 2008 to serve Eastern Singapore. This consisted of 60 total km of sewer tunnels and erection of Changi WRP. Changi was designed to treat 800,000 m3 daily but is able to be expanded up to accommodate 2.4 million m3.

The second phase of building began in 2014. Tunnel boring began in 2017 and concluded in 2023. Construction did face some issues with reduced staff during the pandemic and due to diverse rock types that caused slowdowns for the tunnel boring machines (TBMs). The delay pales in comparison to the system’s long-term legacy, which is expected to be in operation in 2027 and last for 100 years.

The tunnel lining is made of concrete and placed by the TBMs. There is a secondary lining with microbial induced concrete and a high density polyethylene lining to help prevent corrosion. This material choice reduced tunnel thickness, saved costs by a 10% margin and helped cut back on construction time. Advanced sensing and monitoring technology consisting of fiber optic wires track structural integrity and allow engineers to determine where repairs are required. Alternative paths are also built-in to bypass flows during emergencies, blockages and flooding, with the help of tunnel isolation gates.

Phase 2 comprises a 98 km long array of tunnels and link sewers. This extends the network to the western and southern sides of Singapore and adds the Tuas WRP to the system. Upon completion, the Tuas WRP will increase the supply of NEWater by 55%, with 650,000 m3 of household water and 150,000 m3 treated daily. It will be replacing the expansive Ulu Pandan and Jurong WRPs, allowing the latter to be repurposed or demolished. Tuas is positioned to increase energy efficiency, reduce costs and labor, and occupy less land. With the entire system being gravity fed, significantly less pumping is required for the wastewater.

Further, natural ventilation and lighting and easy maintenance access improve overall function and appearance. Tuas bypasses numerous steps of traditional treatment to streamline NEWater production. For example, thermal hydrolysis processes reduce the space needed for biosolids treatment by 40% and increase biogas and energy yield.

Tuas WRP is also being integrated with the Integrated Waste Management Facility (IWMF), a solid waste facility, to take maximize waster recover streams and biogas synthesis. This helps solve another different issue that Singapore faces: landfill overflow. The existing Semaku Landfill is positioned to be completely full by 2035. This will reduce waste sent there by 30% by 2030 through acceptance of food waste.

The design of this system truly includes everything. Many of the choices were selected based upon lessons learned from Phase 1. There are odor treatment facilities that capture and treat any odorous air, which might be emitted from the network. Air management systems maintain a negative pressure system throughout the tunnel. Air jumpers are placed strategically to help push any potential migrating air back into the system so it can travel downstream properly to be treated via activated carbon tanks. All in, Singapore’s water future looks increasingly secure.

Reclaiming Singapore’s water future

Remaining construction tasks include casting of corrosion protection lining, pipe jacking, site reinstatement, mechanical connection and electrical work. As of June 2025, estimates put completion of Phase 2 at 77%. There has been an average of nearly 5,000 workers daily putting in a total of 100 million man hours. Four out of the five tunnel contracts were completed and the last should be finished by now. The aforementioned air jumper and odor control facilities are being tested and should be finished this year. About half of the pipe jacking work for the link sewers has been completed as well. Testing has begun on some digesters at Tuas and mechanical and electrical work has commenced.

Singapore’s work with NEWater and its infrastructure treatment can serve as a model for other countries around the world. It will, considering many milestones are being achieved with the expansion of the WRPs, the treatment process upgrades, advances in the water-waste-energy nexus, and the extreme energy and water savings.

This project advances civil engineering and water engineering and is truly a marvel and a positive advancement to help Singapore meet its high water demands in a sustainable and revolutionary way.