Thames Tideway

What is it?

The Thames Tideway Tunnel (TTT) is a major new sewer that is being built in London.

At 25 kilometres long and around 65 metres deep, the tunnel is the largest infrastructure project undertaken by the UK water sector since privatisation. And its size and scale are unprecedented.

What will it do?

Currently London’s sewers, which catch both sewage and rainfall, can fill up after only 2mm of rain. As there is nowhere for the excess sewage to go, it spills out in to the Thames. Each year around 39 million tonnes of sewage spill out in to the river. The tunnel is the UK Government’s preferred solution to tackle pollution in the River Thames, resulting from the growing population of London and its aging sewer system.

How will it be built?

As part of the project Thames Water has to carry out the preparatory work, such as buying the land it needs.

To protect the delivery of Thames Water’s everyday water and wastewater services, the tunnel will be financed and built by a separate company (the ‘Infrastructure Provider’). Thames Water is responsible for procuring the Infrastructure Provider through a competitive process which is expected to finish in 2015. Once it has been procured the Infrastructure Provider will be regulated by us.

What is Ofwat’s role?

The UK Government decided to proceed with a tunnel solution, our role is to:

  • Make sure that customers get the best value for money and that all costs are kept as low as possible
  • monitor the Infrastructure Provider’s performance to ensure it continues to be incentivised to deliver the project both on time and budget
  • use lessons learned from this to develop future way for regulating and financing large infrastructure projects, like the TTT

How will it affect my bill?

Our role as the economic regulator for the water and wastewater sector in England and Wales means that we set limits on the amount that companies can raise from their customers.  We challenge companies like Thames Water to deliver your services as efficiently as possible.

We have set limits on the total amount that Thames Water can raise from its customers for its preparatory work on the tunnel. Within these limits, it is up to Thames Water to decide how it works out customers’ bills – subject to its other licence conditions .

Where can I get more information?

The guide below provides details on areas which you may want more information or you have a particular question and which organisation can help you.


A diagram explaining the Thames Tideway project