The northern route runs from Stoke Newington in Hackney to New River Head in Islington.

It will allow the transfer of water from our Coppermills Water Treatment Works into the Ring Main, or the transfer of water from Thames Valley sources to Coppermills, in the event of major treatment works failure at Coppermills.

Prior to tunnelling, ground investigations were conducted using boreholes which provided information about the environment through which we would be tunnelling.

Further studies were undertaken to confirm the location of underground services and the presence of deep foundations. Using this information we determined the final routes of the tunnels.

The tunnel is 2.8 miles long and approximately 45 metres below the surface, well below the depth of any service pipes or cables and the London Underground.

We completed the tunnelling work in May 2009. The Northern extension has now been connected into the Ring Main and is in the final stages of commissioning.