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The Tideway Tunnel is a 25km ‘super sewer’ under construction below the River Thames to help reduce sewage pollution in the River Thames and ensure London's wastewater system can meet the demands of a growing population and evolving urban environment.

London, UK
Under construction
Equity ownership
16% 2015
18% 2022
Financial close
August 2015 with a further acquisition in September 2022
Design life
>120 years


The 25km long, 7.2m diameter tunnel runs up to 65 metres below the River Thames and will help to reduce the amount of untreated sewage that is currently discharged into the river. 

New public space created

0 acres

The Tideway Tunnel is one of three components of the London Tideway Improvements which will work conjunctively to reduce polluting discharges into the River Thames by c.37 million cubic metres in a typical year. This will create a healthier environment for London by cleaning up the city’s greatest natural asset, helping the river to sustain a more diverse ecosystem of wildlife. The project is also committed to helping boost the local economy, creating more than 4,000 direct, sustainable jobs during construction, in addition to the local community with three acres of new public space.

Fully operational


The tunnel is being built under three separate construction contracts, each covering a distinct physical section of the network, and will transport a combination of rainwater and untreated sewage to a pumping station located at Abbey Mills, East London, before final treatment in Beckton Sewage Treatment Works. The tunnel is expected to be fully operational in 2025.

Total length of sewer

0 km

Reduction in polluting discharges

c. 0 m

cubic metres in a typical year1
Jobs created during construction

0,000 +

Why we invested

Investment in Tideway enabled INPP to support the funding of a project with clear environmental and social benefits whilst generating long-term, inflation-linked returns from a regulated asset.

Design life

0 years

  • Long-term, inflation-linked revenues: With a 120-year design life, Tideway provides exposure to long-term, inflation-linked revenues regulated by Ofwat
  • Bespoke regulatory arrangement: The framework provides a revenue stream during both the construction and operational periods
Workers in high vis in tideway tunnel
  • Government support package: The package recognises the unique nature of Tideway and provides protection under a range of downside scenarios. This feature, along with the bespoke regulatory arrangement, represents an innovative delivery model which may be used for other large scale public infrastructure projects in the future
  • Positive environmental and social characteristics: Tideway offered INPP the opportunity to be part of the necessary solution to London’s current waste water discharge, creating a healthier living environment and supporting the local economy
  • Management: Very experienced management team, project manager and construction contractors
Sustainable Development Goals (SDGs)

2030 Agenda for Sustainable Development adopted by UN Member States in 2015

SDGs supported:


The Tideway Tunnel aims to positively contribute to the overall health of the River Thames and its aquatic life. The tunnel will reduce the amount of sewage overflow entering the river and will play a key role in supporting a mordernised wastewater management system in London.

Millecent And Battersea Power Station
  • Reduced Sewage Overflow: Once fully operational in 2025, Tideway will work as part of the Thames Tideway Improvements to reduce the amount of polluting discharges entering the River Thames by c.37 million cubic metres in a typical year.
  • Infrastructure Modernisation: The construction of the tunnel is part of a broader effort to modernise the city's aging sewer infrastructure, ensuring London's wastewater management system can meet the demands of a growing population
  • Economic and Social Benefits: Upon completion of the project, Tideway is estimated to have contributed to more than 4,000 direct, sustainable jobs
  • Enhanced Flood Protection: During periods of heavy rainfall, the tunnel can temporarily store excess rainwater and sewage, preventing it from overwhelming the existing sewer system and avoiding flooding in certain areas
  1. The Tideway Tunnel is one component of the London Tideway Improvements which will work conjunctively to achieve this.

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