Background
The Ring Main, which was completed in 1994, forms a complete ring around the major water supply zones in London.
History of the Ring Main
It was designed to improve the speed and efficiency of transferring supplies of drinking water across the capital. Water is moved under gravity, resulting in large energy savings as expensive overland pumping is reduced.
With an average diameter of 2.5 metres, it can carry more than 1,300 million litres of water each day - enough to fill the Albert Hall eight times.
The tunnel is directly connected to our treatment works in Hampton, Ashford Common, Walton and Kempton and allows water to travel in either direction. This means that if a section is taken out of service for maintenance, supplies can still be delivered to each area.
Hampton and Ashford Common are by far the largest works and provide the bulk of the treated water that is fed into the Ring Main.
Why was the Ring Main built?
Since the mid 19th Century, London’s drinking water was pumped from water treatment works to the West and North-East of the city.
As the population of London grew this distribution network gradually became overloaded and a radical solution was needed.
We therefore built the Ring Main by tunnelling around London and linking key points along the route with the smaller diameter distribution network.
The water is now fed into the tunnel from water treatment works and pumped out at pumping stations along the route.
As a result, we no longer needs to pump water 25km across London.
Why are the extensions needed?
Extending the Ring Main will boost our ability to distribute supplies across London to keep up with the capital’s growing demand.
Both new tunnels, one to the north and one to the south of the River Thames, will have the combined capability of carrying an additional 500 million litres of water each day.
The northern route 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.
The southern route will allow up to 200 million litres of water per day to be transferred from the Thames Water Ring Main at Brixton to the Honor Oak reservoirs.
In the event of a major burst main or incident that would drastically affect customers supply we will be able to move bulk amounts of water to the affected areas, minimising the impact of any loss of water supply.
These works are part of our plans for the future management of the Ring Main, providing increased security and flexibility.
How water reaches our customers in London
Water in the Ring Main is not under pumped pressure. It must therefore be brought to the surface using large pumps located in pumpout shafts at pumping stations along the route. The water can then enter the distribution network.
