London Ring Main turns 25

Thames Water celebrates the 25th anniversary of a major feat of engineering which secures water supplies to millions of Londoners.

The Ring Main carries up to 1,300 million litres of water a day - equivalent to 520 Olympic swimming pools - across almost every London borough and was officially opened by Her Majesty The Queen on November 11, 1994. At the time, at 50 miles long, it was the longest tunnel built in the UK, longer than the Channel Tunnel, which opened less than six months earlier, and was dubbed by the national press as ‘the M25 for water’.

The pipe, which took seven years to construct, carries high-quality drinking water from five of Thames Water’s largest water treatment sites around the capital to around 3.5 million customers and was developed to meet the water demand of a growing population. The underground ring is located 30 metres deep and is 2.5 metres wide, and was constructed in a way designed to reduce the need to dig large trenches in multiple roads for pipes to be laid in. Instead, an underground tunnel boring machine was used to create the tunnel without the need for widespread disruption above London’s busy roads. The ring design also means water can flow around the main by gravity without the need for costly mechanical pumps, and the direction of flow can be reversed so water can still move around even while a section is closed for maintenance. A team of ten engineers is now responsible for the operation and upkeep of the main as well as the rolling inspection schedule which ensures every part of the tunnel is checked for leaks and any other defects once every ten years.

Gareth Parry, Thames Water’s head of water production, said: “The Ring Main was an amazing example of innovation in its day, was delivered on time and within budget, and is still a pivotal part of our water supply network in 2019, enabling us to provide world-class tap water to millions of people across London. The fact it was opened by HM The Queen shows just how special it was at the time. It’s a testament to the project team, who had the vision to plan so far into the future, that we still consider it to be one of the most important pieces of infrastructure we rely on today.”

The project team, most of whom have now retired, held a reunion in Reading last month to mark their achievement. At the event, former principle project manager, Roger Remmington said: “I have no doubt that the work we did back then has made the lives of so many people easier. The customers Thames Water serves, of course, but also those who came after us in maintaining the assets. If the Ring Main didn’t exist, I dread to think what the situation would be now in the bid to meet demand. Ultimately, though, it was the people involved who made the project the success it was when so many others in our industry said it couldn’t be done.”

In the 25 years since the Ring Main opened, London’s population has continued to grow and Thames Water is already working on additional large infrastructure options to help meet increased demand. These include plans for a new reservoir in Oxfordshire and the potential transfer of water into the Thames Water area from other parts of the country where supplies aren’t so scarce. The company estimates an extra 2.1 million people will move into its region over the next 25 years. Combined with climate change, this will likely result in a shortfall of 350 million litres of water a day between the amount available and the amount needed by 2045 if no action is taken. By 2100, this shortfall is predicted to increase to 650 million litres a day.